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
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1.
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 24m. 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?
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48
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2.
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5.
Two carts with spring attached to their
ends, collide at time t=10s. Which of the
following curves represents the potential
energy as a function of time?
1. A
2. B
3. C
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Four times as high
Half as high
One-fourth as high
Same height but twice
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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 2v at the bottom,
how many times as high must a new ramp be?
10
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2. Negative work on
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3. No work on the
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70
Consider a weightlifter holding a 500
pound barbell stationary above his head.
The weightlifter is doing:
10
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70
A stone attached to a string is whirled at
constant speed v0 in a horizontal plane as shown.
If the stone starts at position D, is more done
in moving it to a position:
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:
First half > second half
First half = second half
First half < second half
Need more information
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