1. AP Physics Review Ch 4 – Forces and Newton’s Laws of Motion
Be able to apply Newton’s three laws to conceptual questions
Be able to draw free body diagrams and determine the magnitude of each force; from your free body diagram, write an equations for both the x and y axes; if the object is in equilibrium, then F=0; if the object is accelerating, then F=ma
Be able to calculate the normal force (not necessarily equal to mg)
Be able to solve force problems involving friction (fN)
Be able to solve tension problems including objects hanging from cables at various angles and frictionless pulley problems
Be able to calculate the force of gravity and the acceleration due to gravity on different planets
Know the definition of inertia and how it is measured
Be able to identify action-reaction pairs and know that they are always equal
Useful equations to know:

2. A Martian lander is approaching the surface
A Martian lander is approaching the surface. It is slowing its descent by firing its rocket motor. Which is the correct free-body diagram for the lander?
STT5.1

3. A Martian lander is approaching the surface
A Martian lander is approaching the surface. It is slowing its descent by firing its rocket motor. Which is the correct free-body diagram for the lander?
STT5.1

4. A satellite orbits the earth with constant speed at height above the surface equal to the earth’s radius. The magnitude of the satellite’s acceleration is
gon earth.
2gon earth.
4gon earth.
STT12.1

5. A satellite orbits the earth with constant speed at height above the surface equal to the earth’s radius. The magnitude of the satellite’s acceleration is
gon earth.
2gon earth.
4gon earth.
STT12.1

6. The figure shows a binary star system
The figure shows a binary star system. The mass of star 2 is twice the mass of star 1. Compared to , the magnitude of the force is
one quarter as big.
half as big.
twice as big.
four times as big.
the same size.
STT12.2

7. The figure shows a binary star system
The figure shows a binary star system. The mass of star 2 is twice the mass of star 1. Compared to , the magnitude of the force is
one quarter as big.
half as big.
twice as big.
four times as big.
the same size.
STT12.2

8. A planet has 4 times the mass of the earth, but the acceleration due to gravity on the planet’s surface is the same as on the earth’s surface. The planet’s radius is
Re.
2Re.
4Re.
STT12.3

9. A planet has 4 times the mass of the earth, but the acceleration due to gravity on the planet’s surface is the same as on the earth’s surface. The planet’s radius is
Re.
2Re.
4Re.
STT12.3

10. More than your true weight. Less than your true weight.
An elevator that has descended from the 50th floor is coming to a halt at the 1st floor. As it does, your apparent weight is
More than your true weight.
Less than your true weight.
Equal to your true weight.
Zero.
STT5.2

11. More than your true weight. Less than your true weight.
An elevator that has descended from the 50th floor is coming to a halt at the 1st floor. As it does, your apparent weight is
More than your true weight.
Less than your true weight.
Equal to your true weight.
Zero.
STT5.2

12. A rock is attached to a string and hangs from the ceiling of an elevator. As the elevator is moving downward and slowing to a stop, the tension in the string is
greater than the weight of the rock.
less than the weight of the rock.
equal to the weight of the rock.
Zero.

13. A rock is attached to a string and hangs from the ceiling of an elevator. As the elevator is moving downward and slowing to a stop, the tension in the string is
greater than the weight of the rock.
less than the weight of the rock.
equal to the weight of the rock.
Zero.

14. All three 50 kg blocks are at rest
All three 50 kg blocks are at rest. Is the tension in rope 2 greater than, less than or equal to the tension in rope 1?
greater than
less than
equal to
STT8.4

15. All three 50 kg blocks are at rest
All three 50 kg blocks are at rest. Is the tension in rope 2 greater than, less than or equal to the tension in rope 1?
greater than
less than
equal to
STT8.4

16. In the figure to the right is the tension in the string greater than,
less than, or equal to the weight of block B?
Greater than
Less than
Equal to
STT8.5

17. In the figure to the right is the tension in the string greater than,
less than, or equal to the weight of block B?
Greater than
Less than
Equal to
STT8.5

18. the mass of the car. Which of the following statements is true?
A small car is pushing a larger truck that has a dead battery. The mass of the truck is larger than
the mass of the car. Which of the following statements is true?
The car exerts a force on the truck but the truck doesn’t exert a force on the car.
The car exerts a larger force on the truck than the truck exerts on the car.
The car exerts the same amount of force on the truck as the truck exerts on the car.
The truck exerts a larger force on the car than the car exerts on the truck.
The truck exerts a force on the car but the car doesn’t exert a force on the truck.
STT8.6

19. the mass of the car. Which of the following statements is true?
A small car is pushing a larger truck that has a dead battery. The mass of the truck is larger than
the mass of the car. Which of the following statements is true?
The car exerts a force on the truck but the truck doesn’t exert a force on the car.
The car exerts a larger force on the truck than the truck exerts on the car.
The car exerts the same amount of force on the truck as the truck exerts on the car.
The truck exerts a larger force on the car than the car exerts on the truck.
The truck exerts a force on the car but the car doesn’t exert a force on the truck.
STT8.6

20. Is the tension in rope 2 greater than, less than, or equal to the tension in rope 1?
IG8.2
greater than rope 2
less than than rope 2
equal to rope 2

21. Is the tension in rope 2 greater than, less than, or equal to the tension in rope 1?
IG8.2
greater than rope 2
less than than rope 2
equal to rope 2

22. A B
Consider two identical blocks, one resting on a flat surface, and the other resting on an incline. For which case is the normal force greater?
(A) case A
(B) case B
(C) both the same (N = mg)
(D) both the same (0 < N < mg)
(E) both the same (N = 0)
[CORRECT 5 ANSWER]

23. Three blocks of mass 3m, 2m, and m are connected by strings and pulled with constant acceleration a. What is the relationship between the tension in each of the strings? a
(A) T1 > T2 > T3
(B) T1 < T2 < T3
(C) T1 = T2 = T3
(D) all tensions are zero
(E) tensions are random T3 T2 T1 3m 2m m

24. Case 1
Case 2
Below you see two cases: a physics student pulling or pushing a sled with a force F which is applied at an angle q. In which case is the normal force greater?
(A) case 1
(B) case 2
(C) it’s the same for both
(D) depends on the magnitude of the force F
(E) depends on the ice surface

25. In the Atwood machine shown in the diagram, if m1 = 0.40 kg and m2 = 0.60 kg, what is the magnitude of the acceleration of the system? (Ignore friction and the mass of the pulley.) m1 m2
(A) 5.3 m/s2
(B) 3.9 m/s2
(C) 0.98 m/s2
(D) 2.0 m/s2

26. What is the acceleration of the 4 kg mass if there is no friction between the 2kg mass and the horizontal surface?
(A) 0.0 m/s2
(B) 2.0 m/s2
(C) 4.0 m/s2
(D) 6.7 m/s2
(E) 10 m/s2

27. What is the acceleration of the 4 kg mass if there is no friction between the 2kg mass and the horizontal surface?
(A) 0.0 m/s2
(B) 2.0 m/s2
(C) 4.0 m/s2
(D) 6.7 m/s2
(E) 10 m/s2

28. A traffic light of weight 100 N is supported by two ropes as shown in the diagram. What are the tensions in the ropes?
37o
(A) 50 N
(B) 63 N
(C) 66 N
(D) 83 N