Unit 2 Review: Conservation Laws
1. What is momentum?
2. Give an example of an object having momentum.
3. Calculate the momentum for the following objects:
a) An object that has a mass of 200g is moving at 3 m/s
b) An object that has a mass of 12.8 kg is moving at 4.7 m/s
4. What is an impulse?
6. What force is needed to stop a 700kg car in 15.0s? The car is moving at 20 m/s.
7. What is the final speed of a 22,000 kg rocket that is travelling at 110 m/s and then has a 100,000N force acting on it for 25 seconds?
8. Calculate the impulse exerted in each of the following cases:
a) A force of 20 N on a car for 5 seconds
b) The earth pulling down on a 2 kg rock during the 6 seconds it takes to fall freely
10. A 1000kg car was crashed into a garden and stopped. The impulse is 4000Ns and the impact force is 2000N. How long does it take the car to stop?
11. A car starts out at rest. At this point, it’s momentum is _______. The car then has a force of 2000N applied to it in 5 seconds. The change in momentum is ___________. The impulse put on the car is __________. The car now has a momentum of __________. Then a force of 5000N is applied over 2 seconds. This is an impulse of __________ and a change in momentum of ____________. The car now has a momentum of __________. Finally, the force of friction at 7000N to bring the car to a stop. The final momentum of the vehicle is ___________. This means there was a change in momentum of ____________ and an impulse of ___________. The time the brakes were applied was ____________.
12. A 1200kg car was brought from 20m/s to 10m/s over a time period of 6 seconds. Determine the force experienced by the car.
14. How is it possible that the momentum change during a collision is equal and opposite if objects are not the same size?
15. When fighting fires, a firefighter must use great caution to hold a hose that emits large amounts of water at high speeds. Why would such a task be difficult?
16. Fill in the following chart using the conservation of momentum.
Before Collision After Collision
Bat 100
Ball -60 20
Total
18. Find the missing velocity:
19. A 0.112-kg billiard ball moving at 154 cm/s strikes a second billiard ball of the same mass moving in the opposite direction at 46 cm/s. The second billiard ball rebounds and travels at 72 cm/s after the head-on collision. Determine the post-collision velocity of the first billiard ball.
21. How do you know if work is done on an object?
22. Determine if the following situations have work being done, and if the work is positive or negative.
a) A weightlifter pushes up on a heavy barbell of weights.
b) A students pushes against a brick wall, but can’t move it
c) Brakes are applied to slow a moving car to a stop.
23. Why does a vertical force never do work on a horizontally displaced object?
a) A 15 N force is used to push a brick 1.5 meters across a table to the right.
b) A 10N force is used to slow down a moving object over a distance of 10 meters.
c)
Shane carries a 100-N suitcase up three flights of stairs (a height of 12.0 m) and then pushes it with a horizontal force of 40.0 N at a constant speed of 0.8 m/s for a horizontal distance of 32.0 meters. How much work does Ben do on his suitcase during this entire motion?e) Mavis pulls up on an object with a rope at an angle of 30 degrees with 60N of force. The object moves 2.4 meters along the
horizontal.
25. What are the 2 main types of potential energy?
26. What is potential energy?
27. What is kinetic energy?
28. Determine if the following objects have potential or kinetic energy, and calculate them.
b) You throw a football that has a mass of 1.3kg with a speed of 2.3 m/ s
c) A 5kg bowling ball is rolling towards pins at a speed of 1.6 m/s
d) A bird that weighs 3kg is sitting up 3.7 meters in a tree.
29. If an object that is in motion triples its speed, how does this affect its kinetic energy?
30. If an object with potential energy doubles its height, how does this affect its potential energy?
31. What is mechanical energy?
33. What is power?
34. When doing a chin-up, a physics student lifts her 42.0-kg body a distance of 0.25 meters in 2 seconds. What is the power delivered by the student's biceps?
35. What are the internal forces?
37. Which type of forces create a conservation of energy?
38. What happens to the energy of an object if positive work is done on it? Negative work is done on it?
39. If a car is skidding along a highway because someone slams on the brakes, is this positive or negative work? Will this cause the object to lose energy or gain energy? Explain.
41. If an object has a mass of 10kg, and begins at rest at a height of 100m above the ground, what is the object’s mechanical energy at this point? If the object dropped and had a kinetic energy of 5,000J, what would the potential energy be at that point? What height would it be at at this point?
42. What is mechanical advantage?
43. To pull a weed out of a garden, you can apply a force of 80 N to the shovel. The shovel applies a force of 750 N to the weed. What is the mechanical advantage of the shovel?
44. A lever is designed to have a mechanical advantage of 6. If the lever applies a force of 1800 N to an object, how much force is applied to the lever?
46. A stage crew member uses a pulley system to lift scenery for the school play. If he does 850 J of work and the pulley system does 600 J of work, what is the efficiency of the pulley system?