1. Work, power, energy and momentum
Homework and Review Questions

2. Q1
If it takes a child 23 seconds to pull a 27 kg block 45 m using a force of 92 N, what is the:
a) Amount of work done by child on block
b) The power output of the child

3. Question 2
A weightlifter lifts a 400 N weight 0.5 m over his head in 2 seconds. He holds the weight motionless over his head for 2 more seconds.
When is the weightlifter NOT doing work on the weight?
What is the power rate for the weightlifter as she lifts the weight?

4. Question #3
The space shuttle, which was first launched on April , is the world’s first reusable space vehicle. The shuttle is placed in orbit by three engines that do 1.4 x 1013 J of work in 8.5 minutes. What is the power output of these engines?

5. Question 4
A team of horses is hitched to a cart. The team pulls with a force of 471 N. The 1511 N cart travels at constant speed of 3.2 km/hr for 45 minutes. Calculate the work done on the cart and the power delivered by the horses.

6. Q5 A force does work on an object if a component of the force is
perpendicular to the displacement of the object.
parallel to the displacement of the object.
perpendicular to the displacement of the object moves the object along a path that returns the object to its starting position.
parallel to the displacement of the object moves the object along a path that returns the object to its starting position.

7. Q6
Diego pulls a 4.5 kg sled across level snow with a force of 225 N on a rope that is angled 35 degrees above the horizontal. If the sled moves a distance of m in 1.46 minutes, how much work does Diego do? What is his power output? 7

8. Q7 The more powerful the motor is,
the longer the time interval for doing the work is.
the shorter the time interval for doing the work is.
the greater the ability to do the work is.
the shorter the workload is.

9. Q8
Bruno drags a box of mass 58.0 kg along a frictionless floor. Bruno pulls the box from the other side with a force of 11.0 N at an angle of 40.0° above the horizontal. What is the net work done on the box if the displacement of the box is 14.5 m?

10. Q9
A 1345 kg car moving east at 15.7 m/s is struck by a 1923 kg car moving north. They are stuck together and move with an initial velocity of 14.5 m/s at an angle of 63.5 degrees from the east. Was the north moving car exceeding the 20.1 m/s speed limit? 10

11. Q10
During a hurricane, a large tree limb, with a mass of 22.0 kg and a height of 13.3 m above the ground, falls on a roof that is 6.0 m above the ground.
a) Ignoring air resistance, find the kinetic energy of the limb when it reaches the roof.
b) What is the speed of the limb when it reaches the roof? 11

12. Q11
An archer puts a 0.30 kg arrow to the bowstring. An average force of 201 N is exerted to draw the string back 1.3 m
A) Assuming no frictional loss, what speed does the arrow leave the bow?
B) If arrow is shot straight up, how high does it rise? 12

13. Q12
A 3.00 kg toy falls from a height of 10.0 m. Just before hitting the ground, what will be its kinetic energy? (Disregard air resistance. g = 9.81 m/s2.)
98.0 J
29.4 J
0.98 J
294 J

14. Q13
A person’s GPE is 23,546 J on top of a building. The weight of the person is 460 N. What is the height of the building?

15. Question 14
A high jumper jumps 2.04 m. If the jumper has a mass of 67 kg, what is his gravitational potential energy at the highest point of the jump?

16. Question 15 A 45 kg soccer ball was kicked into the air.
Determine the Kinetic energy of the ball if it leaves the foot at 57 m/s.
Determine the GPE of the ball when it is 24m above the ground

17. Q14
A 5500 kg truck accelerates from 4.2 m/s to 7.8 m/s in 15.0 seconds by the application of a constant force.
What is the impulse of the truck?
How large of a force is exerted?

18. Q15
A 50.0 g projectile is launched towards the east with a horizontal velocity of 647 m/s from a 4.65 kg launcher moving in towards the east at 2.00 m/s. What is the velocity of the launcher after the launch?

19. Q16
Kofi, with a mass kg is riding a skateboard with a mass of 2.00 kg and is traveling at 1.2 m/s west. Kofi jumps off and the skateboard stops dead in its tracks. In what direction and with what velocity did he jump?

20. Q17
2 objects collide. Object A has a mass of 3.5 kg and is moving at 40 m/s due east. Object B has a mass of 4.6 m/s and is moving 33 m/s due north. After the collision, Object A is moving at 37 m/s [NE]. How fast is Object B moving after the collison?

21. Q18
Kelli weighs 420 N, and she is sitting on a playground swing that hangs 0.40 m above the ground. Her mom pulls back and releases it when the seat is 1.00 m above the ground.
How fast is Kelli moving when the swing passes through its lowest position?
If Kelli moves through the lowest point at 2.0 m/s, how much work was done on the swing by friction?

22. Q 19
Determine the amount of work done on an object to which the force shown in the graph is applied.