A rock is thrown straight up from the earth\'s surface. Which one of the followi

Question

A rock is thrown straight up from the earth's surface. Which one of the following statements
concerning the net force acting on the rock at the top of its path is true?
(a) The net force is equal to the weight of the rock.
(b) The net force is instantaneously equal to zero newtons.
(c) The net force’s direction changes from up to down.
(d) The net force is greater than the weight of the rock.
(e) The net force is less than the weight of the rock, but greater than zero newtons.

2. A 2.0 N rock slides on a frictionless inclined plane. Which one of the following statements is true concerning the normal force that the plane exerts on the rock?
(a) The normal force is zero newtons.
(b) The normal force is 2.0 N.
(c) The normal force is less than 2.0 N, but greater than zero newtons.
(d) The normal force is greater than 2.0 N.
(e) The normal force increases as the angle of inclination, ?, is increased.
3.7 N 43°
5.9 N

Explanation / Answer

N = mgcos? so (c) The normal force is less than 2.0 N, but greater than zero newtons.
(c) The normal force is less than 2.0 N, but greater than zero newtons.

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