Physics 101 Lecture 07 More Constant Acceleration and

Physics 101: Lecture 07 More Constant Acceleration and Relative Velocity l Today’s lecture will cover more material from Textbook Chapters 3&4 Physics 101: Lecture 7, Pg 1

Last Time l. X and Y directions are Independent! (poor Zip) èPosition, velocity and acceleration are vectors l SF = m a applies in both x and y direction l Projectile Motion èax = 0 in horizontal direction èay = g in vertical direction Physics 101: Lecture 7, Pg 2

Today l More examples of 2 D motion l Newton’s 3 rd l Relative Law Review Motion Physics 101: Lecture 7, Pg 3

Physics 101: Lecture 7, Pg 4

Pulley, Incline and 2 blocks A block of mass m 1 = 2. 6 kg rests upon a frictionless incline as shown and is connected to mass m 1 via a flexible cord over an ideal pulley. What is the acceleration of block m 1 if m 2 = 2. 0 kg? y x Physics 101: Lecture 7, Pg 5

Physics 101: Lecture 7, Pg 8

Newton’s 3 rd Example y x A rope attached to box 1 is accelerating it to the right at a rate of 3 m/s 2. Friction keeps block 2 on top of block 1 w/o slipping. What is the tension in the rope? M 2 M 1 T Physics 101: Lecture 7, Pg 9

Relative Motion Physics 101: Lecture 7, Pg 10

Relative Velocity (review) l Sometimes your velocity is known relative to a reference frame that is moving relative to the earth. èExample 1: A person moving relative to a train, which is moving relative to the ground. èExample 2: a plane moving relative to air, which is then moving relative to the ground. l These velocities are related by vector addition: » vac is the velocity of the object relative to the ground » vab is the velocity of the object relative to a moving reference frame » vbc is the velocity of the moving reference frame relative to the ground Physics 101: Lecture 7, Pg 11

Physics 101: Lecture 7, Pg 12

y Preflight 7. 1 x Three swimmers can swim equally fast relative to the water. They have a race to see who can swim across a river in the least time. Relative to the water, Beth (B) swims perpendicular to the flow, Ann (A) swims upstream, and Carly (C) swims downstream. Which swimmer wins the race? A) Ann B) Beth C) Carly A B C Physics 101: Lecture 7, Pg 13

Think of a swimming pool on a cruise ship When swimming to the other side of the pool, you don’t worry about the motion of the ship ! y A B C x Physics 101: Lecture 7, Pg 14

y ACT Three swimmers can swim equally fast relative to the water. They have a race to see who can swim across a river in the least time. Relative to the water, Beth (B) swims perpendicular to the flow, Ann (A) swims upstream, and Carly (C) swims downstream. Who gets across second Ann or Carly? A) Ann B) Same C) Carly A B C Physics 101: Lecture 7, Pg 15 x

Physics 101: Lecture 7, Pg 16

Swimmer Example y x What angle should Ann take to get directly to the other side if she can swim 5 mph relative to the water, and the river is flowing at 3 mph? A B C Physics 101: Lecture 7, Pg 17

Summary of Concepts l. X and Y directions are Independent! èPosition, velocity and acceleration are vectors l. F = m a applies in both x and y direction l Newton’s 3 rd l Relative Law Motion (Add vector components) Physics 101: Lecture 7, Pg 18

Physics 101: Lecture 7, Pg 19