1. Free Body Diagrams
For any complicated situation,
Isolate each object;
Draw all forces acting on it;
Use for each object.

2. Free Body Diagrams
3) Use for each object.

3. Friction forces:
Contact friction:
(Note that it doesn’t depend on the area.)
Drag:

4. A. Both (1) and (2) are correct;
Three massless pulleys of identical radius R=0.05 m are connected with inextensible cords, as shown in the figure. Pulleys 1 and 3 are attached to a vertical wall and pulley 2 is hanging from a cord that is held by pulleys 1 and 3 and weights of masses m1=m3=5 kg. Weight 2 of mass m2=15 kg is hanging from pulley 2.
Consider the following equations that involve the given masses, the tensions shown in the figure, and the acceleration of weight 1, a.
(1) ;
(2) ;
Which one is correct?
A. Both (1) and (2) are correct;
B. Only (1) is correct, (2) is incorrect;
C. Only (2) is correct, (1) is incorrect;
D. Both (1) and (2) are incorrect.

5. A. Both (1) and (2) are correct;
Three massless pulleys of identical radius R=0.05 m are connected with inextensible cords, as shown in the figure. Pulleys 1 and 3 are attached to a vertical wall and pulley 2 is hanging from a cord that is held by pulleys 1 and 3 and weights of masses m1=m3=5 kg. Weight 2 of mass m2=15 kg is hanging from pulley 2.
Consider the following equations that involve the given masses, the tensions shown in the figure, and the acceleration of weight 1, a.
(1) ;
(2) ;
Which one is correct?
A. Both (1) and (2) are correct;
B. Only (1) is correct, (2) is incorrect;
C. Only (2) is correct, (1) is incorrect;
D. Both (1) and (2) are incorrect.

6. The magnitude of the net force on the wall is: Smaller than ;
Three massless pulleys of identical radius R=0.05 m are connected with inextensible cords, as shown in the figure. Pulleys 1 and 3 are attached to a vertical wall and pulley 2 is hanging from a cord that is held by pulleys 1 and 3 and weights of masses m1=m3=5 kg. Weight 2 of mass m2=15 kg is hanging from pulley 2.
The magnitude of the net force on the wall is:
Smaller than ;
B. Equal to ;
C. Larger than ;
D. Not enough information to answer this question.

7. The magnitude of the net force on the wall is: Smaller than ;
Three massless pulleys of identical radius R=0.05 m are connected with inextensible cords, as shown in the figure. Pulleys 1 and 3 are attached to a vertical wall and pulley 2 is hanging from a cord that is held by pulleys 1 and 3 and weights of masses m1=m3=5 kg. Weight 2 of mass m2=15 kg is hanging from pulley 2.
The magnitude of the net force on the wall is:
Smaller than ;
B. Equal to ;
C. Larger than ;
D. Not enough information to answer this question.

8. The net torque on pulley 2 is in the following direction:
Three massless pulleys of identical radius R=0.05 m are connected with inextensible cords, as shown in the figure. Pulleys 1 and 3 are attached to a vertical wall and pulley 2 is hanging from a cord that is held by pulleys 1 and 3 and weights of masses m1=m3=5 kg. Weight 2 of mass m2=15 kg is hanging from pulley 2.
The net torque on pulley 2 is in the following direction:
A. Into the page;
B. Out of the page;
C. It is zero;
D. Not enough information to answer this question.

9. The net torque on pulley 2 is in the following direction:
Three massless pulleys of identical radius R=0.05 m are connected with inextensible cords, as shown in the figure. Pulleys 1 and 3 are attached to a vertical wall and pulley 2 is hanging from a cord that is held by pulleys 1 and 3 and weights of masses m1=m3=5 kg. Weight 2 of mass m2=15 kg is hanging from pulley 2.
The net torque on pulley 2 is in the following direction:
A. Into the page;
B. Out of the page;
C. It is zero;
D. Not enough information to answer this question.

10. A box B sits in the back of a truck T as the truck slows down for a stop (the box remains motionless relative to the truck). What is the appropriate symbol for the horizontal force that the contact interaction between the box and the truck exerts on the truck?
FNB(T)
FNT(B)
FSFB(T)
FSFT(B)
FKFB(T)

11. A box B sits in the back of a truck T as the truck slows down for a stop (the box remains motionless relative to the truck). What is the appropriate symbol for the horizontal force that the contact interaction between the box and the truck exerts on the truck?
FNB(T)
FNT(B)
FSFB(T)
FSFT(B)
FKFB(T)

12. N7T.4
A child C pulls on a wagon W, using a string S; the wagon moves forward at a constant speed as a result. The third-law partner to the forward force exerted on the wagon is which of the following forces? (R=road)
FST(W)
FWT(S)
FWT(C)
FCT(W)
FWKF(R)
None of the above.

13. N7T.4
A child C pulls on a wagon W, using a string S; the wagon moves forward at a constant speed as a result. The third-law partner to the forward force exerted on the wagon is which of the following forces? (R=road)
FST(W)
FWT(S)
FWT(C)
FCT(W)
FWKF(R)
None of the above.

14. N7T.5
A small car pushes on a disabled truck, accelerating it slowly forward. Each exerts a force on the other as a result of their contact interaction. Which vehicle exerts the greater force on the other?
The car.
The truck.
Both forces have the same magnitude.
The truck doesn’t exert any force on the car.
There is not enough information for a meaningful answer.

15. N7T.5
A small car pushes on a disabled truck, accelerating it slowly forward. Each exerts a force on the other as a result of their contact interaction. Which vehicle exerts the greater force on the other?
The car.
The truck.
Both forces have the same magnitude.
The truck doesn’t exert any force on the car.
There is not enough information for a meaningful answer.

16. N7T.6
A physicist and a chemist are playing tug-of-war. For a certain length of time during the game, the participants are essentially at rest. During this time, each person pulls on the rope (which can be treated as an ideal string) with a force of 350N. What is the tension on the rope?
700N
350N
175N
None of the above

17. N7T.6
A physicist and a chemist are playing tug-of-war. For a certain length of time during the game, the participants are essentially at rest. During this time, each person pulls on the rope (which can be treated as an ideal string) with a force of 350N. What is the tension on the rope?
700N
350N
175N
None of the above

18. N7T.7
Object A (mA=1.0kg) hangs at rest from an ideal string A connected to the ceiling. Object B (mB=2.0kg) hangs at rest from an ideal string B connected to object A. The tension on string A is:
Twice the tension on string B
3/2 times the tension on string B.
Equal to the tension on string B
2/3 the tension of string B
None of the above

19. N7T.7
Object A (mA=1.0kg) hangs at rest from an ideal string A connected to the ceiling. Object B (mB=2.0kg) hangs at rest from an ideal string B connected to object A. The tension on string A is:
Twice the tension on string B
3/2 times the tension on string B.
Equal to the tension on string B
2/3 the tension of string B
None of the above

20. N7T.8
Two people are attempting to break a rope, which will break if the tension on the rope exceeds 360N. If each person can exert a pull of 200N,
They can break the rope if they each take an end and pull.
They can break the rope if they tie one end to the wall and both pull on the other.
They can break the rope if they use either of the strategies above.
They cannot break the rope.

21. N7T.8
Two people are attempting to break a rope, which will break if the tension on the rope exceeds 360N. If each person can exert a pull of 200N,
They can break the rope if they each take an end and pull.
They can break the rope if they tie one end to the wall and both pull on the other.
They can break the rope if they use either of the strategies above.
They cannot break the rope.

22. A spring scale typically indicates the magnitude of the tension force exerted on its bottom hook. What will the scale read in each of the cases shown in the diagram? (Hint: Construct a free-body or a free-particle diagram for the scale in each case.)
49N
98N
186N
None of the above

23. A spring scale typically indicates the magnitude of the tension force exerted on its bottom hook. What will the scale read in each of the cases shown in the diagram? (Hint: Construct a free-body or a free-particle diagram for the scale in each case.)
49N
98N
186N
None of the above