Practice Questions (Chapter 4)

1 .A packing crate slides down an inclined ramp at constant velocity. Thus we can deduce that
a frictional force is acting on it.

(A) a net force is acting on it.
( B) it may be accelerating.
( C) Gravity is not acting on it.


2. You fall while skiing and one ski (of weight W) loosens and slides down an icy slope (assume no friction), which makes an angle q with the horizontal. The force that pushes it down along the hill is

(A) zero; it moves with constant velocity.
(B) W cos q
(C) W sin q
(D) it is not acted on by a gravitational force.


3. A decoration, of mass M, is suspended by a string from the ceiling inside an elevator. The elevator is traveling upward with a constant speed. The tension in the string is

(A) equal to Mg.
(B) less than Mg.
(C) greater than Mg.
(D) impossible to tell without knowing the speed.


4. An object is placed on an inclined plane. The angle of incline is gradually increased until the object begins to slide. The angle at which this occurs is q. What is the coefficient of static friction between the object and the plane?

(A) sin q
(B) cos q
(C) tan q
(D) Cannot determine without knowing the mass of the object.


5. A mass on a string attached to a ceiling is pulled to the side and let go. When the string makes an angle q with the vertical, which of the following is not true?

(A) The weight is down.
(B) The tension equals mg*cos(q).
(C) The tension equals mg*sin(q).
(D) The tension and the weight are never in the same direction.


6. A roller coaster car does a loop-the-loop. When it is upside down at the very top, which of the following is true?

(A) The normal force and the weight are in opposite directions.
(B) The normal force and the weight are perpendicular to each other.
(C) The weight is zero.
(D) The normal force and the weight are in the same direction.


7. A roller coaster car does a loop-the-loop. When it is right-side up at the very bottom, which of the following is true?

(A) The normal force and the weight are in opposite directions.
(B) The normal force and the weight are perpendicular.
(C) The weight is zero.
(D) The normal force and the weight are in the same direction.


8. A 2 kg box sits on a 3 kg box which sits on a 5 kg box. The 5 kg box rests on a table top. What is the normal force exerted on the 5 kg box by the table top?

(A) 19.6 N
(B) 29.4 N
(C) 49 N
(D) 98 N


9. A 2 kg box sits on a 3 kg box which sits on a 5 kg box. The 5 kg box rests on a table top. What is the normal force exerted by the 5 kg box on the 3 kg box?

(A) 19.6 N
(B) 29.4 N
(C) 49 N
(D) 98 N


10. A 5 kg (4.9 N) book rests on your desk. Which of the following answers is not correct?

(A) The normal force on the book equals its weight because of Newton's First Law.
(B) The normal force on the book equals its weight because of Newton's Second Law.
(C) The normal force on the book equals the weight because of Newton's Third Law.


11. 5 kg (4.9 N) book rests on your desk. What is the reaction force to the 4.9 N weight (force) of the book?

(A) The 4.9 N normal force from the table on the book.
(B) The 4.9 N reaction force from the book on the table.
(C) The weight of the earth.
(D) A 4.9 N force on the Earth.


12. You stand on a bathroom scale in an elevator accelerating upwards and it reads 200 Newtons. Which of the following is true?

(A) You weigh 200 Newtons.
(B) The scale exert a 200 N force on you.
(C) The acceleration of the elevator is 20.4 m/s^2.
(D) None of the above are correct.


13. During the investigation of a traffic accident, police find skid marks 90 m long. They determine the coefficient of friction between the car's tires and the roadway to be 0.5 for the prevailing conditions. To find the speed of the car you must

(A) know the mass of the car.
(B) find the acceleration of the car.
( C) know the mass of the car and find the acceleration of the car.


14. An object moves left to right (right is positive) with speed decreasing at a constant rate and
its acceleration is positive.

(A) the net force on it is decreasing.
(B) the net force on it is increasing.
(C) its acceleration is negative.


15. A car pulls on a rope tied to a tree with a force of 1000 Newtons. Which of the following is not true.

(A) The rope pulls on the tree with a force of 1000 Newtons.
(B) The tree pulls on the rope with a force of 1000 Newtons.
(C) The tension in the rope is 2000 Newtons.
(D) The tension in the rope is 1000 Newtons.



16. A 5 kg block and a 10 kg block slide down a frictionless incline and
they both have the same acceleration.

(A) the 5 kg block has an acceleration of twice that of the 10 kg block.
(B) the 10 kg block has an acceleration of twice that of the 5 kg block.
(C) their acceleration depends on the normal force.