Homework

Physics 101 - Homework 7

Instructions: Complete this form and click submit. The answers will be posted on the course home page after the due date and before the next exam. If you want to change any of your answers after you click submit, then go back and give your answers again and click submit.

Your Name: e.g. John Doe

Your Campus ID: e.g. 12345678

Your SFA Email Address: e.g. doejd@titan.sfasu.edu

Due Date 11/30/2007 5:00PM

0. Some of the questions below may have been modified from the in-class handout. Try to answer these first without looking at the handout, then study the handout, modify your answers if necessary and click Submit.
I understand
I do not understand

1. What impulse is needed to stop a 1200-kg car traveling at 20 m/s?
(a) 20 N.s
(b) 1200 N.s
(c) 60 N.s
(d) 24,000 N.s

2. A force times time is most appropriately called
(a) a torque
(b) an impulse
(c) an angular momentum
(d) a change in momentum

3. Which of the following is true about momentum?
(a) it is a vector
(b) it is a product of mass times velocity
(c) impulses are required to change it
(d) all of the above
(e) none of the above

4. A car with a mass of 2000 kg moves at 10 m / s. Calculate the braking force needed to bring the car to a halt in 5 seconds.
(a) 100000N
(b) 4000N
(c) 20000N
(d) 40 N

5. The car moving at 50 kilometers/hour skids 10 meters with locked brakes. How far will the car skid with locked brakes if it is traveling at 150 kilometers/hour?
(a) 20 meters
(b) 60 meters
(c) 90 meters
(d) 120 meters
(e) 180 meters

6. At what point in its motion is the kinetic energy of a pendulum bob a minimum?
(a) at the highest points in its motion
(b) at the lowest point in its motion
(c) half way between the highest and lowest points in its motion

7. A 1-kg object rests on a table 1 m above the floor. What is the gravitational potential energy in Joules of the object with respect to the floor?
(a) 1
(b) 9.8
(c) 32
(d) 11.8
(e) 0

8. When a car is braked to a stop, its kinetic energy is transformed to
(a) stopping energy.
(b) potential energy.
(c) heat energy.
(d) energy of rest.

9. If you push on an immovable wall for an hour, is there any work done on the wall?
(a) Yes
(b) No

10. Can a body have kinetic energy without having momentum?
(a) Yes
(b) No

11. A torque acting on an object tends to produce
(a) equilibrium.
(b) rotation.
(c) linear motion.
(d) stability.

12. A coin and a ring roll down an incline starting at the same time from rest. The one to reach the bottom first will be the
(a) ring
(b) coin
(c) both reach the bottom at the same time

13. The center of mass of a body can be outside of the body
(a) True
(b) False

14. When a spinning ice skater draws her arms in close to her body, she starts to spin faster. This is an example of
(a) external torque friction
(b) Newton's second law
(c) conservation of angular momentum
(d) spin impulse

15. Which is the larger force?
(a) the force that the earth exerts on the moon
(b) the force that the moon exerts on the earth
(c) neither

16. A merchant of gold should_________ at a high altitude and ___________ at a low altitude.
(a) buy, sell
(b) sell, buy
(c) buy or sell, buy or sell

17. When the distance between two stars decreases by half, the force between them
(a) decreases by one-quarter
(b) decreases by one-half
(c) increases to twice as much
(d) increases to four times as much
(e) stays the same

18. The planet Jupiter is about 300 times as massive as earth, yet on its surface you would weight only about 3 times as much. This is because
(a) your mass is 100 times less on Jupiter.
(b) Jupiter is significantly farther from the sun.
(c) Jupiter's radius is 10 times the earth's radius.
(d) you are 100 times more weightless there.
(e) none of these.

Need more examples or assistance? If you have a new text book then you may be able to access tutorials and online quizes at www.PhysicsPlace.com. The Access Code for this site is normally included in the first few pages of the book. See Dr. B for help during these office hours.

Your Name:	e.g. John Doe
Your Campus ID:	e.g. 12345678
Your SFA Email Address:	e.g. doejd@titan.sfasu.edu
Due Date	11/30/2007 5:00PM

0. Some of the questions below may have been modified from the in-class handout. Try to answer these first without looking at the handout, then study the handout, modify your answers if necessary and click Submit. I understand I do not understand
	1. What impulse is needed to stop a 1200-kg car traveling at 20 m/s? (a) 20 N.s (b) 1200 N.s (c) 60 N.s (d) 24,000 N.s
	2. A force times time is most appropriately called (a) a torque (b) an impulse (c) an angular momentum (d) a change in momentum
	3. Which of the following is true about momentum? (a) it is a vector (b) it is a product of mass times velocity (c) impulses are required to change it (d) all of the above (e) none of the above
	4. A car with a mass of 2000 kg moves at 10 m / s. Calculate the braking force needed to bring the car to a halt in 5 seconds. (a) 100000N (b) 4000N (c) 20000N (d) 40 N
	5. The car moving at 50 kilometers/hour skids 10 meters with locked brakes. How far will the car skid with locked brakes if it is traveling at 150 kilometers/hour? (a) 20 meters (b) 60 meters (c) 90 meters (d) 120 meters (e) 180 meters
	6. At what point in its motion is the kinetic energy of a pendulum bob a minimum? (a) at the highest points in its motion (b) at the lowest point in its motion (c) half way between the highest and lowest points in its motion
	7. A 1-kg object rests on a table 1 m above the floor. What is the gravitational potential energy in Joules of the object with respect to the floor? (a) 1 (b) 9.8 (c) 32 (d) 11.8 (e) 0
	8. When a car is braked to a stop, its kinetic energy is transformed to (a) stopping energy. (b) potential energy. (c) heat energy. (d) energy of rest.
	9. If you push on an immovable wall for an hour, is there any work done on the wall? (a) Yes (b) No
	10. Can a body have kinetic energy without having momentum? (a) Yes (b) No
	11. A torque acting on an object tends to produce (a) equilibrium. (b) rotation. (c) linear motion. (d) stability.
	12. A coin and a ring roll down an incline starting at the same time from rest. The one to reach the bottom first will be the (a) ring (b) coin (c) both reach the bottom at the same time
	13. The center of mass of a body can be outside of the body (a) True (b) False
	14. When a spinning ice skater draws her arms in close to her body, she starts to spin faster. This is an example of (a) external torque friction (b) Newton's second law (c) conservation of angular momentum (d) spin impulse
	15. Which is the larger force? (a) the force that the earth exerts on the moon (b) the force that the moon exerts on the earth (c) neither
	16. A merchant of gold should_________ at a high altitude and ___________ at a low altitude. (a) buy, sell (b) sell, buy (c) buy or sell, buy or sell
	17. When the distance between two stars decreases by half, the force between them (a) decreases by one-quarter (b) decreases by one-half (c) increases to twice as much (d) increases to four times as much (e) stays the same
	18. The planet Jupiter is about 300 times as massive as earth, yet on its surface you would weight only about 3 times as much. This is because (a) your mass is 100 times less on Jupiter. (b) Jupiter is significantly farther from the sun. (c) Jupiter's radius is 10 times the earth's radius. (d) you are 100 times more weightless there. (e) none of these.