SMDEP Physics Potential Energy Fridays Mechanics Quiz No

SMDEP Physics Potential Energy

Friday’s Mechanics Quiz • No calculators needed/allowed • No clickers needed • Don’t memorize formulas – Any formulas needed will be provided • Mostly qualitative, conceptual questions • Length: About 30 minutes • Material: Kinematics, Mechanics, Energy – Circular motion, friction, springs – NOT: vectors, dot products, momentum • Grades not instant • Also: Midcourse evaluations – What would you change about the course?

Resources • Textbook: especially end-of-chapter “Questions” • New web site – http: //www. astro. yale. edu/krines/smdep/ – Powerpoints of first two weeks, more to come • Email – KR: krines@astro. yale. edu – AC: andrew. cahoon@yale. edu • Office hours: Wed. (today) 5: 30 -6: 30 in Harkness Cafeteria

Survey: From what source do you get the news (most of the time)? 1. 2. 3. 4. 5. 6. 7. Network/Cable TV Newspaper AM radio FM radio Internet news source Other source I’m oblivious to the world!

A spring-loaded toy dart gun is used to shoot a dart straight up in the air, and the dart reaches a maximum height of 24 m. The same dart is shot straight up a second time from the same gun, but this time the spring is compressed only half as far before firing. How far up does the dart go this time, neglecting friction and assuming an ideal spring? 1. 2. 3. 4. 5. 48 m 24 m 12 m 6 m Not enough info

Two carts with spring attached to their ends, collide at time t=10 s. Which of the following curves represents the potential energy as a function of time? 1. A 2. B 3. C U A B 10 s t C 0 of 5 10

70 A block initially at rest is allowed to slide down a frictionless ramp and attains a speed v at the bottom. To achieve a speed 2 v at the bottom, how many times as high must a new ramp be? 1. 2. 3. 4. 5. 6. 7. 0 Same height Twice as high Four times as high Half as high One-fourth as high Same height but twice as long Same height but 4 times as long 10

70 Consider a weightlifter holding a 500 pound barbell stationary above his head. The weightlifter is doing: 1. Positive work on the barbell 2. Negative work on the barbell 3. No work on the barbell 0 10

70 A stone attached to a string is whirled at constant speed v 0 in a horizontal plane as shown. If the stone starts at position D, is more done in moving it to a position: A 1. 2. 3. 4. 5. 0 A D B C C D None of the above; no work is done by the string B 10

A puck moving across a horizontal surface experiences constant negative acceleration due to friction, and comes to rest after 12 seconds. How does the energy lost in the first 6 seconds compare to the energy lost in the last 6 seconds: 1. 2. 3. 4. 0 of 5 First half > second half First half = second half First half < second half Need more information : 10