A rock is thrown straight up with an initial velocity of 20.0 m/s.Ignore energy lost to air friction.How high will the rock rise?
A) 41.0 m
B) 10.2 m
C) 20.4 m
D) 11.5 m

Question

Quizplus · Accepted Answer

The height that the rock will reach can be found using the kinematic equation: 
Δy = v0t + (1/2)at^2 
where Δy is the change in height, v0 is the initial velocity, a is the acceleration due to gravity (-9.8 m/s^2), and t is the time it takes for the rock to reach its highest point (when its final velocity is 0 m/s). 
Using the given initial velocity, v0 = 20.0 m/s, and the fact that the final velocity at the highest point is 0 m/s, we can find the time it takes for the rock to reach its highest point: 
0 = 20.0 m/s - 9.8 m/s^2 * t_highest 
t_highest = 20.0 m/s / 9.8 m/s^2 = 2.04 s 
Plugging this into the same kinematic equation gives: 
Δy = (20.0 m/s)(2.04 s) + (1/2)(-9.8 m/s^2)(2.04 s)^2 
Δy = 20.4 m 
Therefore, the rock will reach a height of 20.4 meters.

A Rock Is Thrown Straight Up with an Initial Velocity