CutnellJohnson Physics 7 th edition Classroom Response System

4. 2. 1. A pipe is bent into the shape shown and oriented so

4. 2. 2. If an object is moving can you conclude there are forces

4. 2. 3. A child is driving a bumper car at an amusement park.

4. 3. 1. A car of mass m is moving at a speed 3

4. 3. 2. A car is driving due south through a parking lot and

4. 3. 3 The graph shows the velocities of two objects as a function

4. 3. 4. The drawing shows a steel ball flying at constant velocity from

4. 3. 5. A 912 -kg car is being driven down a straight, level

4. 4. 1. An object is moving due south at a constant velocity. Then,

4. 5. 1. A water skier is being pulled by a rope attached to

4. 5. 2. A large crate is lifted vertically at constant speed by a

4. 5. 3. An astronaut is on a spacewalk outside her ship in “gravity-free”

4. 7. 1. A cannon fires a ball vertically upward from the Earth’s surface.

4. 7. 2. If an object at the surface of the Earth has a

4. 7. 3. Two objects that may be considered point masses are initially separated

4. 7. 4. Two satellites of masses m and 2 m are at opposite

4. 7. 5. An astronaut, whose mass on the surface of the Earth is

4. 8. 1. A free-body diagram is shown for the following situation: a force

4. 8. 2. A free-body diagram is shown for the following situation: a force

4. 8. 3. Consider the three cases shown in the drawing in which the

4. 8. 4. Consider the situation shown in the drawing. Block A has a

4. 9. 1. On a rainy evening, a truck is driving along a straight,

4. 9. 2. Jennifer is pushing a heavy box up a rough inclined surface

4. 9. 3. A crate of mass m is at rest on a horizontal

4. 9. 4. A crate of mass m is at rest on a horizontal

4. 9. 5. Three pine blocks, each with identical mass, are sitting on a

4. 9. 6. Jake bought a new dog and is carrying a new dog

4. 10. 1. Some children are pulling on a rope that is raising a

4. 10. 2. One end of a string is tied to a tree branch

4. 10. 3. A rock is suspended from a string. Barbara accelerates the rock

4. 11. 1. Consider the following: (i) the book is at rest, (ii) the

4. 11. 2. A block of mass M is hung by ropes as shown.

4. 11. 3. A team of dogs pulls a sled of mass 2 m

4. 12. 1. A man stands on a bathroom scale that indicates his weight

4. 12. 2. In a moving elevator, a woman standing on a bathroom scale

4. 12. 3. A block of mass m is pressed against a wall with

4. 12. 4. A force of magnitude F pushes a block of mass 2

4. 12. 5. A box is held by a rope on a frictionless inclined

4. 12. 6. Two identical cement cylinders are attached to the opposite ends of

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Cutnell/Johnson Physics 7 th edition Classroom Response System Questions Chapter 4 Forces and Newton’s Laws of Motion Interactive Lecture Questions

4. 2. 1. A pipe is bent into the shape shown and oriented so that it is sitting horizontally on a table top. You are looking at the pipe from above. The interior of the pipe is smooth. A marble is shot into one end and exits the other end. Which one of the paths shown in the drawing will the marble follow when it leaves the pipe? a) 1 b) 2 c) 3 d) 4 e) 5

4. 2. 2. If an object is moving can you conclude there are forces acting on it? If an object is at rest, can you conclude there are no forces acting on it? Consider each of the following situations. In which one of the following cases, if any, are there no forces acting on the object? a) A bolt that came loose from a satellite orbits the earth at a constant speed. b) After a gust of wind has blown through a tree, an apple falls to the ground. c) A man rests by leaning against a tall building in downtown Dallas. d) Sometime after her parachute opened, the sky diver fell toward the ground at a constant velocity. e) Forces are acting on all of the objects in choices a, b, c, and d.

4. 2. 3. A child is driving a bumper car at an amusement park. During one interval of the ride, she is traveling at the car’s maximum speed when she crashes into a bumper attached to one of the side walls. During the collision, her glasses fly forward from her face. Which of the following statements best describes why the glasses flew from her face? a) The glasses continued moving forward because there was too little force acting on them to hold them on her face during the collision. b) During the collision, the girl’s face pushed the glasses forward. c) The glasses continued moving forward because the force of the air on them was less than the force of the girl’s face on them. d) During the collision, the car pushed the girl forward causing her glasses to fly off her face. e) During the collision, the wall pushed the car backward and the girl reacted by pushing her glasses forward.

4. 3. 1. A car of mass m is moving at a speed 3 v in the left lane on a highway. In the right lane, a truck of mass 3 m is moving at a speed v. As the car is passing the truck, the driver notices that the traffic light ahead has turned yellow. Both drivers apply the brakes to stop ahead. What is the ratio of the force required to stop the truck to that required to stop the car? Assume each vehicle stops with a constant deceleration and stops in the same distance x. a) 1/9 b) 1/3 c) 1 d) 3 e) 9

4. 3. 2. A car is driving due south through a parking lot and its speed is monitored. Prepare a graph of the car’s speed versus time using the following data: Segment A: the car begins at rest and uniformly accelerates to 5 m/s in an elapsed time of 2 s. Segment B: for the next 10 seconds, the car moves at a constant speed of 5 m/s. Segment C: during the next 2 seconds, the car uniformly slows to 3 m/s. Segment D: for the next 4 seconds, the car travels at a constant speed of 3 m/s. Using your graph, determine which one of the following statements is false. a) Net forces act on the car during intervals A and C. b) No net force acts on the car during interval B. c) Opposing forces may be acting on the car during interval C. d) The magnitude of the net force acting during interval A is less than that during C. e) Opposing forces may be acting on the car during interval B.

4. 3. 3 The graph shows the velocities of two objects as a function of time. During the intervals A, B, and C indicated, net forces , , and act on the two objects, respectively. If the objects have equal mass, which one of the following choices is the correct relationship between the magnitudes of the three net forces? a) FA > FB = FC b) FC > FA > FB c) FA < FB < FC d) FA = FB = FC e) FA = FC > FB

4. 3. 4. The drawing shows a steel ball flying at constant velocity from point A to point B in a region of space where the effects of gravity are negligible. During the short time that passes as the ball flies past point B, a magnet exerts a force on it in the direction of the magnet. Which of the following trajectories does the ball follow beyond point B? a) 1 b) 2 c) 3 d) 4 e) 5

4. 3. 5. A 912 -kg car is being driven down a straight, level road at a constant speed of 31. 5 m/s. When the driver sees a police cruiser ahead, she removes her foot from the accelerator. After 8. 00 s, the speed of the car is 24. 6 m/s, which is the posted speed limit. What is the magnitude of the average net force acting on the car during the 8. 00 s interval? a) 55. 2 N b) 445 N c) 629 N d) 787 N e) 864 N

4. 4. 1. An object is moving due south at a constant velocity. Then, a net force directed due west acts on the object for a short time interval, after which, the net force on the object is zero newtons. Which one of the following statements concerning the object is necessarily true? a) The final velocity of the object will be directed south of west. b) The final velocity of the object will be directed due south. c) The direction of acceleration of the object while the force was being applied was south of west. d) The magnitude of the object’s acceleration while the force was being applied was dependent on the object’s initial velocity. e) The change in the object’s velocity while the force was applied was directed south of east.

4. 5. 1. A water skier is being pulled by a rope attached to a speed boat moving at a constant velocity. Consider the following four forces: (1) the force of the boat pulling the rope, (2) the force of the skier pulling on the rope, (3) the force of the boat pushing the water, and (4) the force of the water pushing on the boat. Which two forces are an “actionreaction” pair that is consistent with Newton’s third law of motion? a) 1 and 2 b) 2 and 3 c) 2 and 4 d) 3 and 4 e) 1 and 4

4. 5. 2. A large crate is lifted vertically at constant speed by a rope attached to a helicopter. Consider the following four forces that arise in this situation: (1) the weight of the helicopter, (2) the weight of the crate, (3) the force of the crate pulling on the earth, and (4) the force of the helicopter pulling on the rope. Which one of the following relationships concerning the forces or their magnitudes is correct? a) The magnitude of force 4 is greater than that of force 2. b) The magnitude of force 4 is greater than that of force 1. c) Forces 3 and 4 are equal in magnitude, but oppositely directed. d) Forces 2 and 4 are equal in magnitude, but oppositely directed. e) The magnitude of force 1 is less than that of force 2.

4. 5. 3. An astronaut is on a spacewalk outside her ship in “gravity-free” space. Initially, the spacecraft and astronaut are at rest with respect to each other. Then, the astronaut pushes to the left on the spacecraft and the astronaut accelerates to the right. Which one of the following statements concerning this situation is true? a) The astronaut stops moving after she stops pushing on the spacecraft. b) The velocity of the astronaut increases while she is pushing on the spacecraft. c) The force exerted on the astronaut is larger than the force exerted on the spacecraft. d) The spacecraft does not move, but the astronaut moves to the right with a constant speed. e) The force exerted on the spacecraft is larger than the force exerted on the astronaut.

4. 7. 1. A cannon fires a ball vertically upward from the Earth’s surface. Which one of the following statements concerning the net force acting on the ball at the top of its trajectory is correct? a) The net force on the ball is instantaneously equal to zero newtons at the top of the flight path. b) The direction of the net force on the ball changes from upward to downward. c) The net force on the ball is less than the weight, but greater than zero newtons. d) The net force on the ball is greater than the weight of the ball. e) The net force on the ball is equal to the weight of the ball.

4. 7. 2. If an object at the surface of the Earth has a weight W, what would be the weight of the object if it was transported to the surface of a planet that is one-sixth the mass of Earth and has a radius one third that of Earth? a) 3 W b) 4 W/3 c) W d) 3 W/2 e) W/3

4. 7. 3. Two objects that may be considered point masses are initially separated by a distance d. The separation distance is then decreased to d/3. How does the gravitational force between these two objects change as a result of the decrease? a) The force will not change since it is only dependent on the masses of the objects. b) The force will be nine times larger than the initial value. c) The force will be three times larger than the initial value. d) The force will be one third of the initial value. e) The force will be one ninth of the initial value.

4. 7. 4. Two satellites of masses m and 2 m are at opposite sides of the same circular orbit about the Earth. Which one of the following statements is true? a) The magnitude of the gravitational force is greater for the satellite of mass 2 m than it is for the other satellite. b) The magnitude of the gravitational force is the same for both satellites; and it is greater than zero newtons. c) Since the satellites are moving at a constant velocity, the gravitational force on the satellites must be zero newtons. d) The magnitude of the gravitational force is greater for the satellite of mass m than it is for the other satellite. e) The satellite of mass 2 m must move faster in the orbit than the other and eventually they will be on the same side of the Earth.

4. 7. 5. An astronaut, whose mass on the surface of the Earth is m, orbits the Earth in the space shuttle at an altitude of 450 km. What is her mass while orbiting in the space shuttle? a) 0. 125 m b) 0. 25 m c) 0. 50 m d) 0. 75 m e) m

4. 8. 1. A free-body diagram is shown for the following situation: a force pulls on a crate of mass m on a rough surface. The diagram shows the magnitudes and directions of the forces that act on the crate in this situation. represents the normal force on the crate, represents the acceleration due to gravity, and represents the frictional force. Which one of the following expressions is equal to the magnitude of the normal force? a) P f / b) P f c) P f mg d) mg e) zero

4. 8. 2. A free-body diagram is shown for the following situation: a force pulls on a crate that is sitting on a rough surface. The force is directed at an angle above the horizontal direction. The diagram shows the magnitudes and directions of the forces that act on the crate in this situation. represents the normal force on the crate, represents the weight of the crate, and represents the frictional force. Which one of the following actions would result in an increase in the normal force? a) Decrease the angle . b) Increase the magnitude of. c) Decrease the coefficient of friction. d) Decrease the magnitude of . e) Increase the coefficient of friction

4. 8. 3. Consider the three cases shown in the drawing in which the same force is applied to a box of mass M. In which case(s) will the magnitude of the normal force on the box equal (F sin + Mg)? a) Case One only b) Case Two only c) Case Three only d) Cases One and Two only e) Cases Two and Three only

4. 8. 4. Consider the situation shown in the drawing. Block A has a mass 1. 0 kg and block B has a mass 3. 0 kg. The two blocks are connected by a very light rope of negligible mass that passes over a pulley as shown. The coefficient of kinetic friction for the blocks on the ramp is 0. 33. The ramp is angled at = 45. At time t = 0 s, block A is released with an initial speed of 6. 0 m/s. What is the tension in the rope? a) 11. 8 N b) 7. 88 N c) 15. 8 N d) 13. 6 N e) 9. 80 N

4. 9. 1. On a rainy evening, a truck is driving along a straight, level road at 25 m/s. The driver panics when a deer runs onto the road and locks the wheels while braking. If the coefficient of friction for the wheel/road interface is 0. 68, how far does the truck slide before it stops? a) 55 m b) 47 m c) 41 m d) 36 m e) 32 m

4. 9. 2. Jennifer is pushing a heavy box up a rough inclined surface at a constant speed by applying a horizontal force F as shown in the drawing. The coefficient of kinetic friction for the box on the inclined surface is k. Which one of the following expressions correctly determines the normal force on the box? a) b) c) d) e)

4. 9. 3. A crate of mass m is at rest on a horizontal frictionless surface. Another identical crate is placed on top of it. Assuming that there is no slipping of the top crate as a horizontal force is applied to the bottom crate, determine an expression for the static frictional force acting on the top crate. a) f = F b) c) d) e)

4. 9. 4. A crate of mass m is at rest on a horizontal frictionless surface. Another identical crate is placed on top of it. Assuming a horizontal force is applied to the bottom crate, determine an expression for the minimum static coefficient of friction so that the top crate does not slip. a) b) c) d) e)

4. 9. 5. Three pine blocks, each with identical mass, are sitting on a rough surface as shown. If the same horizontal force is applied to each block, which one of the following statements is false? a) The coefficient of kinetic friction is the same for all three blocks. b) The magnitude of the force of kinetic friction is greater for block 3. c) The normal force exerted by the surface is the same for all three blocks. d) Block 3 has the greatest apparent area in contact with the surface. e) If the horizontal force is the minimum to start block 1 moving, then that same force could be used to start block 2 or block 3 moving.

4. 9. 6. Jake bought a new dog and is carrying a new dog house on the flatbed of his brand new pickup truck. Jake isn’t sure if he should tie the house down, but he doesn’t want it to scratch the paint if it should slide during braking. During the trip home, Jake will travel along straight, level roads and have to stop from a maximum speed of 21 m/s in a distance of 29 m. What is the minimum coefficient of static friction between the dog house and the paint that is required to prevent it from sliding? Compare your answer to the actual coefficient of friction of 0. 35 to determine if the dog house should be tied down. a) 0. 22, no need to tie the house down b) 0. 30, no need to tie the house down c) 0. 35, he may want to tie it down just in case d) 0. 56, the house needs to be tied down e) 0. 78, the house needs to be tied down

4. 10. 1. Some children are pulling on a rope that is raising a bucket via a pulley up to their tree house. The bucket containing their lunch is rising at a constant velocity. Ignoring the mass of the rope, but not ignoring air resistance, which one of the following statements concerning the tension in the rope is true? a) The magnitude of the tension is zero newtons. b) The direction of the tension is downward. c) The magnitude of the tension is equal to that of the weight of the bucket. d) The magnitude of the tension is less than that of the weight of the bucket. e) The magnitude of the tension is greater than that of the weight of the bucket.

4. 10. 2. One end of a string is tied to a tree branch at a height h above the ground. The other end of the string, which has a length L = h, is tied to a rock. The rock is then dropped from the branch. Which one of the following statements concerning the tension in the string is true as the rock falls? a) The tension is independent of the magnitude of the rock’s acceleration. b) The magnitude of the tension is equal to the weight of the rock. c) The magnitude of the tension is less than the weight of the rock. d) The magnitude of the tension is greater than the weight of the rock. e) The tension increases as the speed of the rock increases as it falls.

4. 10. 3. A rock is suspended from a string. Barbara accelerates the rock upward with a constant acceleration by pulling on the other end of the string. Which one of the following statements concerning the tension in the string is true? a) The tension is independent of the magnitude of the rock’s acceleration. b) The magnitude of the tension is equal to the weight of the rock. c) The magnitude of the tension is less than the weight of the rock. d) The magnitude of the tension is greater than the weight of the rock. e) The tension decreases as the speed of the rock increases as it rises.

4. 11. 1. Consider the following: (i) the book is at rest, (ii) the book is moving at a constant velocity, (iii) the book is moving with a constant acceleration. Under which of these conditions is the book in equilibrium? a) (i) only b) (ii) only c) (iii) only d) (i) and (ii) only e) (ii) and (iii) only

4. 11. 2. A block of mass M is hung by ropes as shown. The system is in equilibrium. The point O represents the knot, the junction of the three ropes. Which of the following statements is true concerning the magnitudes of the three forces in equilibrium? a) F 1 + F 2 = F 3 b) F 1 = F 2 = 0. 5×F 3 c) F 1 = F 2 = F 3 d) F 1 > F 3 e) F 2 < F 3

4. 11. 3. A team of dogs pulls a sled of mass 2 m with a force. A second sled of mass m is attached by a rope and pulled behind the first sled. The tension in the rope is. Assuming frictional forces are too small to consider, determine the ratio of the magnitudes of the forces and , that is, P/T. a) 3 b) 2 c) 1 d) 0. 5 e) 0. 33

4. 12. 1. A man stands on a bathroom scale that indicates his weight is W. The man is standing on the scale inside an elevator when it is at rest. What will the scale read when the elevator is moving upward at a constant velocity v? a) The scale will read a value that is slightly less than W. b) The scale will read a value that is slightly greater than W. c) The scale will read the same value W. d) The scale will read a value that is much greater than W. e) The scale will read zero newtons.

4. 12. 2. In a moving elevator, a woman standing on a bathroom scale notices that the reading on the scale is significantly larger than when the elevator was at rest. The elevator itself only has two forces acting on it: the tension in a cable and the force of gravity. Which one of the following statements is false concerning this situation? a) The elevator is uniformly accelerating. b) The elevator’s speed is increasing as it moves upward. c) The tension in the cable exceeds the weight of the elevator and its contents. d) The elevator could be moving upward at constant speed. e) The elevator could be moving downward with decreasing speed.

4. 12. 3. A block of mass m is pressed against a wall with an initial force and the block is at rest. The coefficient of static friction for the block against the wall is equal to 0. 5. The coefficient of kinetic friction is less than the coefficient of static friction. If the force is equal to the weight of the block, which one of the following statements is true? a) The block will continue to remain at rest because the force of static friction is two times the weight of the block. b) The block will slide down the wall because the force of static friction is only equal to one-half of the block’s weight. c) The block will accelerate at 9. 8 m/s 2 down the wall. d) The block will slide down the wall at constant speed. e) The block will accelerate at less than 4. 9 m/s 2 down the wall.

4. 12. 4. A force of magnitude F pushes a block of mass 2 m, which in turn pushes a block of mass m as shown. The blocks are accelerated across a horizontal, frictionless surface. What is the magnitude of the force that the smaller block exerts on the larger block? a) F/3 b) F/2 c) F d) 2 F e) 3 F

4. 12. 5. A box is held by a rope on a frictionless inclined surface as shown. What will the magnitude of the acceleration of the box be if the rope breaks? a) g b) g sin c) g cos d) g tan e) zero m/s 2

4. 12. 6. Two identical cement cylinders are attached to the opposite ends of a spring scale via very light ropes (the mass of which can be neglected) that run over frictionless pulleys as shown. When the same scale was suspended from the ceiling and one of the cylinders was hung from it, the scale indicated its weight is W newtons. What will the scale read in the configuration shown? a) zero newtons b) W/2 newtons c) W newtons d) 2 W newtons e) 4 W newtons