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Motion and Force Chapter 2 Study Guide Answer Key
1. A reference point is a location to which you can compare other locations
2. Speed is measured using the following units: km/hr, mi/hr, m/s
3. You need to know direction and distance from a reference point to measure an object’s position.
4. A girl runs 100 meters in 20 seconds. What is her speed? (show your work)
5 m/s
5. Velocity is speed in a specific direction
6. Acceleration is the rate at which velocity changes with time.
7. If you increase force then acceleration increases
8. Newton’s second law states that if you apply the same force but increase the mass of an object then the
acceleration of the box will decrease
9. Centripetal force is any force that is keeping an object moving in a circle.
10. According to Newton’s third law when an object exerts a force on another object, the second object
exerts a force back on the first object that is equal in size and opposite in direction.
11. A balanced force is equal forces on an object that do not cause the object to move.
12. Action/reaction forces are force pairs that act on two different objects.
13. Give an example of an action/reaction force. (answers will vary) You jump up in the air. The action
is your feet applying force to the ground and the reaction is the ground pushing on your feet.
14. Momentum is a measure of mass in motion.
15. Collision is a situation in which two objects in close contact transfer energy and momentum
16. What does it mean if momentum is conserved? The total momentum after a collision is equal to the
total momentum before the collision.
17. Force can be described as a push or a pull
18. A net force is all the forces acting on an object.
19. You need to know mass and acceleration to calculate force.
20. Inertia is the resistance of an object to a change in its motion.
21. Give an example of zero net force being applied to an object (answers will vary – anything that is a
balanced force)
22. Conservation of momentum is when the only forces acting on objects are action/reaction pairs.
23. An unbalanced force is forces that are applied unequally and cause an object to have motion.
24. You have to apply an unbalanced force to change the motion of an object.
25. Write a sentence relating velocity and momentum The greater the velocity, the greater the
momentum.
26. What force is being applied to a 60 kg cart that is
accelerating at 4.2 m/s2? (show all of your work)
27. What is the mass of a box that is being pushed at
an acceleration of 5 m/s2 with a force of 70 N?
F = ma
m = F/a
F = 60 kg x 4.2 m/s2
m = 70 N / 5 m/s2
F = 252 N
m = 350 Kg
28. What is the velocity of a car that has a mass of
1400 kg and a momentum of 3080 kg m/s? v = P / m
29. What is the velocity of a car that has a mass of
1500 kg and a momentum of 3300 kg m/s? v = P / m
V=p/m
V=p/m
V = 3080 Kg m/s / 1400 Kg
V = 3300 Kg m/s / 1500 Kg
V = 2.2 m/s
V = 2.2 m/s
Answer the following questions on a separate sheet of paper
30. Two bumper cars collide. Use the collision of the cars to help you explain the conservation of
momentum. Use the following terms in your answer: conservation of momentum, mass, velocity,
outside forces.
Before the collision, each bumper car has a mass and a velocity. These can be used to calculate the
total momentum of the system. After the collision, the cars will have different velocities. If you
calculate the new total momentum using these new velocities, the law of conservation of momentum
states the new total momentum is equal to the original total momentum. If momentum is not
conserved, there are outside forces acting on the system.
31. A marathon runner wants to choose the best shoe for a race. She knows that she should consider the
mass of the shoe as she makes her decision. Which of Newton’s laws should she consider and why?
According to Newton’s second law of motion, she should choose the shoe with the least mass. This is
because mass is closely related to inertia. The more massice an object, the more inertia it has, and the
more force it takes to get the object moving. It will take more force for the runner to move a more
massive shoe than a lighter one.
32. Use Newton’s three laws of motion to explain why a child should not ride in the front seat of a car that
has air bags.
In a collision, the child’s inertia would keep him going forward at the speed the car had been going,
according to Newton’s first law. When the air bag deploys, the child hits the air bag with a force
equal to his mass times his acceleration, according to Newton’s second law, while the air bag hits the
child with the force it exerts as it expands. The action-reaction force of this collision, according to
Newton’s third law, is great enough to cause harm to, or even kill, a small child.