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Chapter 3 Review: Forces, Newton’s Laws and Momentum
1.
Complete vocabulary review sets 1 – 4 at the end of chapter 3 on page 62.
Set 1: 1.E 2. C 3.A 4.B 5.F
Set 2: 1.B 2.F 3.D 4.C 5. A
Set 3: 1.B 2.F 3. D 4.E 5.C
Set 4: 1.D 2.A 3.B 4. C 5.F
2.
Define the term force, and give some examples of forces.
A force is any push or pull that has the ability to change the motion of an object.
3.
Describe how Newton’s First Law (the law of inertia) applies to wearing seatbelts in a car.
Since objects in motion tend to stay in motion, when a car is stopped suddenly or speeds up suddenly, your
body tends to resist the change in motion and the seatbelts help keep you in place.
4.
Which has more inertia, a 1-kilogram baseball or a 10-kilogram bowling ball?
The 10 kg bowling ball has more inertia.
5.
Which two units combine to make a Newton?
A Newton is equal to a kg x m/s2
6.
Show the equation for Newton’s Second Law with the units for each variable.
Force (N) = mass (kg) x acceleration (m/s2)
7.
According to Newton’s Second Law, what will happen to the acceleration of an object when:
a. The mass is increased: The acceleration will decrease
b. The Force is increased: The acceleration will increase
8.
Zoo keepers lift a cage that holds a lion. The total mass of the lion and cage is 175 kg and the acceleration of the lion and cage in 0.657 m/s2.What
force is needed to produce this acceleration of the lion and the cage?
F = ma = (175kg) (0.657m/s2) = 114.975 N
9.
A car pulled by a tow truck has an acceleration of 2.0 m/s2. What is the mass of the car if the net force on the car is 3,000 N east?
m=F/a = (3,000 N) / (2.0 m/s2) = 1500 kg
10. If a helicopter’s mass is 4,500 kg and the net force on it is 18,000 N upward, what is its acceleration?
a=F/m = (18,000N) / (4,500 kg) = 4 m/s2
11. Explain the difference between mass and weight.
Mass is a fundamental property that describes the amount of matter in an object, while weight is the effect of
gravity on the mass. Mass will never change, however, weight will when the gravity changes.
12. Show the equation for Weight with the units for each variable.
Weight (N) = mass (kg) x gravity (m/s2)
13. On the surface of the Earth, what is the acceleration due to gravity?
The acceleration due to gravity on Earth is 9.8 m/s2
14. A wrestler weighs in for his first match on the moon. Will the athlete weigh more or less on the moon than he does on Earth? Will he have more
mass?
Although the wrestler’s mass would not change, the wrestler would weigh less on the moon, because the
gravity on the moon is less than the gravity on Earth.
15. What is the weight of a 2.25 kg book bag on the Earth?
W = mg = (2.25 kg)(9.8 m/s2) = 22.05 N
16. If that same textbook weighs 14.625 N on another planet, what is the acceleration due to gravity there?
(Remember mass is still the same) g = W/m = (14.625 N) /(2.25 kg) = 6.5 m/s2
17. What is friction?
Friction is a force that occurs between 2 objects in contact with one another and always resists the forward
motion of an object.
18. Explain the effect that viscosity has on friction?
More viscosity would result in more resistance, thus, more friction.
19. Explain the effect that uneven surfaces have on friction?
An uneven surface would also result in more resistance, thus, more friction.
20. Using a specific type of friction, explain how a skydiver opening her parachute slows her down.
When the skydiver opens her parachute, she is increasing the amount of air friction action on her, and that
resistance that the air is exerting on her allows her to fall slower.
21. During gym, two teams are playing Tug of War. The pink team on the left side of the rope has three players – one who pulls with 2 N of force and
two who pull with 1 N of force. The blue team, on the right side of the rope also has 3 players, two who pull with 2 N of force and one who pulls
with 1 N of force. Sketch the scenario. What is the net force on the rope?
The net force is 2 N to the right.
22. Fill in the blanks in the following statements:
a. Forces always occur in pairs
b. Each force in an action-reaction pair of forces is equal magnitude
c. Each force in an action-reaction pair of forces is opposite in direction
23. Describe the action reaction forces of a swimmer swimming the length of a pool.
Action: The swimmer pulls the water behind her.
Reaction: The water pushes the swimmer forward
24. Describe the action reaction forces of a bird flying up through the air.
Action: The bird pushes the air down
Reaction: The air then pushes the bird up.
25. Show the equation for momentum with the units for each variable.
Momentum (kg x m/s) = mass (kg) x velocity (m/s)
26. A 0.5-kg snowball is traveling at 40 m/s. What is the snowball's momentum?
p = mv = 0.5 x 40 = 20 kgxm/s
27. A ball is moving at 6.0 m/s and has a momentum of 24.0 kg·m/s. What is the ball's mass?
M = p/v = 24/6 = 4 kg
28. A bullet has a momentum of 12 m/s kg and a mass of 0.050kg . What is its velocity?
v = p/m = 12/0.050 = 240 m/s
29. What happens to the total amount of momentum when two objects collide with one another?
It is conserved during collisions.
30. A 1,250 kg car is is stopped at a traffic light. A 3550 kg truck moving at 8.33 m/s hits the car from behind. If the truck comes to a complete stop,
how fast will the car be moving after the collision?
Use the equation : m1v1 + m2v2 = m1v1 + m2v2
(3550)(8.33) + (1250)(0) = (3550)(0) + (1250) v2
V2 = 23.67 m/s