# Physics Homework Help

1. Why do a slow-moving loaded truck and a speeding rifle bullet have a large momentum?
2. NASA’s Langley Research Centre has been experimenting with the use of air bags to soften the landings of crew exploration vehicles (CEV) on land. What stopping time will be required in order to safely stop a 7250 kg CEV moving at 7.65 m/s with an average force of 426,000 N (an average force of 6 Gs)?
3. An automobile accident causes both the driver and passenger front airbags to deploy.
1. If the vehicle travelled at a speed of 88.6 km/h is now at rest, find the change in momentum for both the 68.4 kg adult driver and the 34.2 kg child passenger.
2. The adult took 0.564 s and the child took 0.260 s to come to rest. Find the force that the airbag exerted on each individual. Explain why airbags tend to be dangerous to children.
4. An automobile accident investigator needs to determine the initial westerly velocity of a Jeep (m=1720 kg) that may have been speeding before colliding head-on with a Volkswagen (m=1510 kg) that was moving with a velocity of 75.7 km/h east. The speed limit on this road is 90 km/h. After the collision, the Jeep and the Volkswagen stuck together and continued to travel with a velocity of 15.5 km/h west.
1. Find the initial westerly velocity of the Jeep.
2. Was the Jeep speeding?
5. Define the first and second conditions of equilibrium in your own words.
6. Eight people are involved in a tug-of-war. The blue team members pull the rope with the forces of 220 N, 340 N, 180 N, and 560 N. Three members of the red team pull it with the forces of 250 N, 160 N, and 420 N. With what force must the fourth person pull the rope to maintain equilibrium?
7. A scaffold supports a bricklayer and bricks weighing 450 lb. If the force at one end support is 290 lb, what is the supporting force at the other?
8. A torque wrench reads 25 lb ft.
1. If its length is 1.0 ft, what force is being applied to the wrench?
2. What is the force if the length is doubled?
9. A gardener pushes a mower at a distance of 900 m while mowing the yard. The handle of the mower makes an angle of 40.0° with the ground. The gardener exerts a force of 35.0 N along the handle of the mower. How much work does the gardener do in mowing the lawn?

PH2530: Module 2 Conservation of Energy and Momentum

Exercise 2.1

Forces and the Conservation of Energy and Momentum

10. A 475 kg prestressed concrete beam is to be raised 10.0 m in 24.0 s. How many kilowatts of power is needed for the job?
11. A hammer falls from a scaffold on a building 50.0 m above the ground. Find its speed as it hits the ground.
12. A 1250 kg wrecking ball is lifted to a height of 12.7 m above its resting point. When the wrecking ball is released, it swings toward an abandoned building and makes an indentation of 43.7 cm in the wall.
1. What is the potential energy of the wrecking ball at a height of 12.7 m?
2. What is its kinetic energy at the time of striking the wall?
3. If the wrecking ball transfers all of its kinetic energy to the wall, how much force does the wrecking ball apply to the wall?
4. Why should a wrecking ball strike a wall at the lowest point in its swing?
13. Why do a slow-moving loaded truck and a speeding rifle bullet have a large momentum?
14. NASA’s Langley Research Centre has been experimenting with the use of air bags to soften the landings of crew exploration vehicles (CEV) on land. What stopping time will be required in order to safely stop a 7250 kg CEV moving at 7.65 m/s with an average force of 426,000 N (an average force of 6 Gs)?
15. An automobile accident causes both the driver and passenger front airbags to deploy.
1. If the vehicle travelled at a speed of 88.6 km/h is now at rest, find the change in momentum for both the 68.4 kg adult driver and the 34.2 kg child passenger.
2. The adult took 0.564 s and the child took 0.260 s to come to rest. Find the force that the airbag exerted on each individual. Explain why airbags tend to be dangerous to children.
16. An automobile accident investigator needs to determine the initial westerly velocity of a Jeep (m=1720 kg) that may have been speeding before colliding head-on with a Volkswagen (m=1510 kg) that was moving with a velocity of 75.7 km/h east. The speed limit on this road is 90 km/h. After the collision, the Jeep and the Volkswagen stuck together and continued to travel with a velocity of 15.5 km/h west.
1. Find the initial westerly velocity of the Jeep.
2. Was the Jeep speeding?
17. Define the first and second conditions of equilibrium in your own words.
18. Eight people are involved in a tug-of-war. The blue team members pull the rope with the forces of 220 N, 340 N, 180 N, and 560 N. Three members of the red team pull it with the forces of 250 N, 160 N, and 420 N. With what force must the fourth person pull the rope to maintain equilibrium?
19. A scaffold supports a bricklayer and bricks weighing 450 lb. If the force at one end support is 290 lb, what is the supporting force at the other?
20. A torque wrench reads 25 lb ft.
1. If its length is 1.0 ft, what force is being applied to the wrench?
2. What is the force if the length is doubled?
21. A gardener pushes a mower at a distance of 900 m while mowing the yard. The handle of the mower makes an angle of 40.0° with the ground. The gardener exerts a force of 35.0 N along the handle of the mower. How much work does the gardener do in mowing the lawn? PH2530: Module 2 Conservation of Energy and Momentum

Exercise 2.1

Forces and the Conservation of Energy and Momentum

22. A 475 kg prestressed concrete beam is to be raised 10.0 m in 24.0 s. How many kilowatts of power is needed for the job?
23. A hammer falls from a scaffold on a building 50.0 m above the ground. Find its speed as it hits the ground.
24. A 1250 kg wrecking ball is lifted to a height of 12.7 m above its resting point. When the wrecking ball is released, it swings toward an abandoned building and makes an indentation of 43.7 cm in the wall.
1. What is the potential energy of the wrecking ball at a height of 12.7 m?
2. What is its kinetic energy at the time of striking the wall?
3. If the wrecking ball transfers all of its kinetic energy to the wall, how much force does the wrecking ball apply to the wall?
4. Why should a wrecking ball strike a wall at the lowest point in its swing?

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