Quiz 5, Physics 2a, Oct 29 2010
Double check that you bubble in your code number correctly.
If there’s a mistake, your score will be lowered –as a penalty.
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VERSION A
1. You push an eraser, which weighs 0.5N , a distance of 2m across a tabletop. The
eraser is pushed with a horizontal force at a small, negligible, constant velocity. The
coefficient of friction between the eraser and the table is µK = 0.2. Approximately
what is the force of friction?
(a) 0.5N
(b) 0.2N
(c) 0.1N
(d) 0.01N
2. Same setup. How much work have you done on the eraser?
(a) 1J
(b) −1J
(c) 0.1J
(d) 0.2J
3. You push a loaded grocery cart with force F~ = 40Nbi − 30N b
j, and it undergoes a
displacement ~s = 10mbi + 2mb
j. How much work did you do on the cart?
(a) 340J
(b) −340J
(c) 400J
(d) −400J
4. A 4kg watermelon carried to the top of Urey Hall, up many flights of stairs. The
distance traveled along the stairs was 40m, and the elevation gain to the top of Urey
Hall is 20m. Approximately much work was done carrying the watermelon to the top
of Urey?
(a) 160J
(b) 1600J
(c) 80J
(d) 800J
5. The watermelon is now dropped off the top of Urey (height 20m). What is the kinetic
energy of the watermelon when it hits the ground (ignoring air resistance).
(a) 1600J
(b) 800J
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(c) 500J
(d) 200J.
6. Same setup, but this time the watermelon queen at the top of Urey throws the melon
horizontally outward, with a velocity of 5m/s. What is the watermelon’s kinetic
energy when it hits the ground?
(a) 800J
(b) 850J
(c) 900J
(d) 1600J
7. Applying a force of 30N to a spring compresses it a distance of 0.1m. What is the
spring’s constant k? (We’re intentionally omitting the appropriate MKS units.)
(a) 300
(b) 10
(c) 30
(d) 3
8. Same setup. How much work is required to compress the spring by 0.1m?
(a) 1.5J
(b) 3J
(c) 6J
(d) 1J
9. You do 400J of work, pushing with a constant force on a 8kg cart. Your force is
directed in the same direction as the cart’s motion and you can ignore friction. What
is the velocity of the cart right after you’ve done all that work?
(a) 50m/s
(b) 25m/s
(c) 20m/s
(d) 10m/s.
10. This setup is like one of your homework problems: a 3kg block is on a table, and
connected with a string, which goes over a pulley, and tied to the other end of the
string is a 2kg block. The 2kg block slides on the table without friction (this differs
from your homework question). What is the approximate velocity of the blocks after
the 2kg block has descended 0.5m?
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(a) 2m/s
(b) 4m/s
(c) 8m/s
(d) 10m/s.
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