1. A person standing on a horizontal floor feels two forces: the downward pull of gravity and the upward supporting force from the floor. These two forces

(A) have equal magnitudes and form an action! reaction pair.
(B) have equal magnitudes but do not form an action/reaction pair.
(C) have unequal magnitudes and form an action/reaction pair.
(D) have unequal magnitudes and do not form an action/reaction pair.
(E) None of the above

2. A person who weighs 800 N steps onto a scale that is on the floor of an elevator car. If the elevator accelerates upward at a rate of 4.9 m/s². what will the scale read?

(A) 400N
(B) 800N
(C) 1000 N
(D) 1200 N
(E) 1600 N

3. A frictionless inclined plane of length 20 m has a maximum vertical height of 5 m. If an object of mass 2 kg is placed on the plane, which of the following best approximates the net force it feels?

(A) 5 N
(B) 10 N
(C) 15 N
(D) 20 N
(E) 30 N

4. A 20 N block is being pushed across a horizontal table by an 18 N force. If the coefficient of kinetic friction between the block and the table is 0.4, find the acceleration of the block.

(A) 0.5 m/s²
(B) 1 m/s²
(C) 5 m/s²
(D) 7.5 m/s²
(E) 9 m/s²

5. The coefficient of static friction between a box and a ramp is 0.5. The ramp’s incline angle is 30°. If the box is placed at rest on the ramp, the box will

(A) accelerate down the ramp.
(B) accelerate briefly down the ramp but then slow down and stop.
(C) move with constant velocity down the ramp.
(D) not move.
(E) cannot be determined from the information given

6. Assuming a frictionless, massless pulley, determine the acceleration of the blocks once they are released from rest.

7. If all of the forces acting on an object balance so that the net force is zero, then

(A) the object must be at rest.
(B) the object’s speed will decrease.
(C) the object will follow a parabolic trajectory.
(D) the object’s direction of motion can change, but not its speed.
(E) None of the above

8. A block of mass m is at rest on a frictionless, horizontal table placed in a laboratory on the surface of the earth. An identical block is at rest on a frictionless, horizontal table placed on the surface of the Moon. Let F be the net force necessary to give the Earth-bound block an acceleration of a across the table. Given that g_Moon is one-sixth of g_Earth the force necessary to give the Moon-bound block the same acceleration a across the table is

(A) F/12
(B) F/6
(C) F/3
(D) F
(E) 6F

9. A crate of mass 100 kg is at rest on a horizontal floor. The coefficient of static friction between the crate and the floor is µ_s = 0.4, and the coefficient of kinetic friction is µ_k = 0.3. A force F of magnitude 344 N is then applied to the crate, parallel to the floor. Which of the following is true?

(A) The crate will accelerate across the floor at 0.5 m/s².
(B) The static friction force, which is the reaction force to F as guaranteed by Newton’s Third Law, will also have a magnitude of 344 N.
(C) The crate will slide across the floor at a constant speed of 0.5 m/s.
(D) The crate will not move.
(E) None of the above

10. Two crates are stacked on top of each other on a horizontal floor; Crate #1 is on the bottom, and Crate #2 is on the top. Both crates have the same mass. Compared to the strength of the force F₁ necessary to push only Crate #1 at a constant speed across the floor, the strength of the force F₂ necessary to push the stack at the same constant speed across the floor is greater than F₁ because

(A) the force of the floor on Crate #1 is greater.
(B) the coefficient of kinetic friction between Crate #1 and the floor is greater.
(C) the force of kinetic friction, but not the normal force, on Crate #1 is greater.
(D) the coefficient of static friction between Crate #1 and the floor is greater.
(E) the weight of Crate #1 is greater.

11. An object moves at constant speed in a circular path. Which of the following statements is/are true?

I. The velocity is constant.
II. The acceleration is constant.
III. The net force on the object is zero since its speed is constant.

(A) II only
(B) I and III only
(C) II and III only
(D) I and II only
(E) None of the above

Questions 12-13:

A 60 cm rope is tied to the handle of a bucket which is then whirled in a vertical circle. The mass of the bucket is 3 kg.

12. At the lowest point in its path, the tension in the rope is 50 N. What is the speed of the bucket?

(A) 1 m/sec
(B) 2 m/sec
(C) 3 m/sec
(D) 4 m/sec
(E) 5 m/sec

13. What is the critical speed below which the rope would become slack when the bucket reaches the highest point in the circle?

(A) 0.6 m/sec
(B) 1.8 m/sec
(C) 2.4 m/sec
(D) 3.2 m/sec
(E) 4.8 m/sec

14. An object moves at a constant speed in a circular path of radius r at a rate of 1 revolution per second. What is its acceleration?

(A)0
(B) (2 p² s^-2)r
(C) (2 p² s^-2)r²
(D) (4 p² s^-2)r
(E) (4 p² s^-2)r²