A man leans over the edge of a cliff and throws a rock upward at 4.9 m/s.Neglecting air resistance,two seconds later the rock's speed is
A)zero.
B)4)9 m/s.
C)9)8 m/s.
D)14.7 m/s.
E)none of the above

Question

Quizplus · Accepted Answer

The acceleration due to gravity is 9.8 m/s^2. When an object is thrown vertically upward, its initial velocity is positive and its acceleration is negative (due to the opposing direction of gravity).

Using the kinematic equation for velocity with constant acceleration, we can solve for the final velocity of the rock after 2 seconds:

v = v0 + at 
v = 4.9 m/s - 9.8 m/s^2 (2 s) 
v = - 14.7 m/s

Note that the negative sign on the velocity indicates that the rock is moving downward after reaching its maximum height. However, the question only asks for the rock's speed, which is the magnitude of its velocity regardless of direction. Therefore, the answer is 14.7 m/s.

A Man Leans Over the Edge of a Cliff and Throws