PHYS 231 Quiz #2

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Multiple choice: 1 pt. each

1. An object is traveling at constant velocity. What can you conclude?

A. The sum of the forces on the object point in the direction of the object's motion.

B. There are no forces acting on the object whatsoever.

*C. The sum of the forces on the object add up to zero.

D. None of the above can be concluded from such information.

2. The weight of an object is the force of gravity on the object. Which of the following is true for two identical objects, one on the moon, one on the earth?

*A. They have the same mass.

B. They have the same weight.

C. Both A and B.

D. Neither A nor B.

3. Newton's Third Law (the action-reaction law) states that when you slap somebody across the face with your hand,

A. that person will slap you with his hand across your face with equal force.

B. the acceleration of that person's face is equal to the force of the hand divided my the mass of the face.

*C. that person's face will slap your hand with equal force.

D. the total force on the face is zero.

4. A book is resting on a table. The reaction force to the book's weight is

A. the normal force of the table upward on the book.

*B. the gravitational force of the book on the earth.

C. the gravitational force of the earth on the table.

D. the normal force of the earth on the table.

5. A person is on an elevator that is decelerating as it reaches the top floor. While this is happening, he feels that his weight is

*A. lighter.

B. heavier.

C. the same.

D. zero.

6. A box of mass m is stationary on the ground. You apply a force parallel to the ground in an attempt to drag it. Taking friction into account, the box doesn't budge until you apply a force equal to

A.

*B.

C. mg

D. whatever. Any force will move the box.

7. A heavy object does not budge until a certain force is applied to it parallel to the ground. When the object moves, it takes less force to keep it moving. From this, we can conclude that

*A.

B.

C.

D.

8. You swing around your head a ball that's attached to a string. In addition to gravity and tension of the string, which forces are acting on the ball?

A. A centrifugal force outward

B. A centripetal force inward

C. Both A and B

*D. Neither A nor B.

9. A student attempts to drag a desk of mass 20 kg across the floor by applying a force parallel to the floor. If it takes 49 N to get the desk moving and 39 N to keep it moving, what are and for the desk on the floor?(2 pts)