C. Work Take Home Quiz
300 Points Possible ( 10 points/question)
For Questions #1-9, Match the unit or expression to the physical quantity.
a) friction f) mgy k) ftlb
b) J/s g) 1/2 mv2 l) -kx
c) dyne cm h) dimensionless m) weight
d) N m i) N/m n) ftlb/s
e) 550 ftlb/s j) 3.6 MJ
2. kinetic energy
3. potential energy
4. conservative force
5. non-conservative force
6. spring constant
8. Hooke's Law
10. Two men, Joel and Jerry, push against a wall. Jerry stops after 10 min, while Joel is able to push for 5 min longer. Compare the work they do.
a. Joel does 50% more work than Jerry.
b. Jerry does 50% more work than Joel.
c. Joel does 75% more work than Jerry.
d. Neither of them do any work.
11. You lift a 10-lb physics book up in the air a distance of 1 ft, at a constant velocity of 0.5 ft/s. The work done by gravity is
a. +10 ftlb
b. -10 ftlb
c. +5 ftlb
d. -5 ftlb
12. The area under the curve, on a Force-position (F-x) graph, represents
b. kinetic energy.
13. Which of the graphs illustrates Hooke's Law?
a. graph A
b. graph B
c. graph C
d. graph D
14. Which of the above graphs represent a spring which gets less stiff the more it is stretched?
a. graph A
b. graph B
c. graph C
d. graph D
15. A 10-kg mass, hung onto a spring, causes the spring to stretch 2.0 cm. The spring constant is
a. 49 N/cm
b. 5.0 N/cm
c. 0.20 N/cm
d. 0.0020 N/cm
16. A simple pendulum, consisting of a mass m and a string, swings upward, making an angle q with the vertical. The work done by the tension force is: (Hint: Ask yourself this question: “Does the ‘bob’ move because of the tension in the string?” If yes, then there is work done by the tension, if not, then the answer is zero)
c. mg cos q
d. mg sin q
17. Matthew pulls his little sister Sarah in a sled on a flat, icy surface (assume no friction), with a force of 60 N at an angle of 37o upward from the horizontal. If he pulls her a distance of 12 m, the work he does is
a. 185 J
b. 433 J
c. 575 J
d. 720 J
18. A container of water is lifted vertically 3 m, then returned to its original position. If the total weight is 30 N, how much work was done?
a. 45 J
b. 90 J
c. 180 J
d. No work was done.
19. A truck weighs twice as much as a car, and is moving at twice the speed of the car. Which statement is true about the truck's kinetic energy (K) compared to that of the car?
a. All that can be said is that the truck has more K.
b. The truck has twice the K of the car.
c. The truck has 4 times the K of the car.
d. The truck has 8 times the K of the car.
20. A toy rocket, weighing 10 N, blasts off from ground level. At the exact top of its trajectory, its energy is 140 J. To what vertical height does it rise?
a. 1.4 m
b. 14. m
c. 1.4 km
d. None of the above
21. You slam on the brakes of your car in a panic, and skid a certain distance on a straight, level road. If you had been traveling twice as fast, what distance would the car have skidded, under the same conditions?
a. It would have skidded 4 times farther.
b. It would have skidded twice as far.
c. It would have skidded ÚÄ times farther.
d. It is impossible to tell from the information given.
22. On the accompanying diagram of a pendulum, at what position is the potential energy maximum?
23. On the accompanying diagram of a pendulum, at what position is the kinetic energy maximum?
24. Which of the following is not a unit of work?
25. If both mass and the velocity of a ball are each tripled, the kinetic energy is increased by a factor of:
26. Consider a plot of the displacement (x) vs applied force (F) for an ideal elastic spring. The slope of the curve would be: (Hint: When you read this question, be sure you understand which unit is on which axis. In other words, refer to your knowledge of _____ vs. ______ graphs. Which one is on the x-axis and which is on the y-axis?)
a. the spring constant
b. the reciprocal of the spring constant
c. the acceleration of gravity
d. the reciprocal of the acceleration of gravity
e. none of the above
27. The work energy theorem says
a. the net work done is equal to the initial kinetic energy less the final energy.
b. final kinetic energy plus the net work done is the initial kinetic energy.
c. the net work done plus the initial kinetic energy is the final kinetic energy.
d. the net work done plus the final kinetic energy is the initial kinetic energy.
e. the net work done minus the initial kinetic energy is the final kinetic energy.
28. Consider the work lab that we did in class. Is there any difference in the amount of force it takes to pull the cart up the ramp at a constant velocity and the force it takes to just hold the cart in place (for example: Say you pull the cart half-way up the ramp and just let the force meter register its readings as you hold still)
a. yes, there is a difference. The force is greater when you pull it than when you hold it still.
b. yes, there is a difference. The force is lower when you pull it than when you hold it still.
c. No, there is no difference
29. Still consider that work lab (Remember you were dragging an object up ramps of varying distance, but the HEIGHT WAS ALWAYS THE SAME). What is the only circumstance(s) under which the force of friction has NO EFFECT on the work done by the system. (Answer may be more than one letter)
a. When you are pulling a wooden block up the ramp (which does have friction).
b. When you are pulling a wooden block up a frictionless ramp.
c. When you are pulling a cart on wheels up a frictionless ramp.
d. When you are pulling a cart on wheels up a friction ramp.
30. Again with the work lab (will he ever stop asking questions???!! - NOPE, SORRY). What happens to the normal force on the cart as you raise the ramp to a vertical position.
a. Normal force increases towards mg
b. Normal force decreases towards 0
c. Normal force doesn’t exist for carts on wheels.