A rock is thrown downward from an unknown height above the ground with an initial speed of 10 m/s. It strikes the ground 3.0 s later. Determine the initial height of the rock above the ground.
A) 44 m
B) 14 m
C) 74 m
D) 30 m
E) 60 m

Question

Quizplus · Accepted Answer

Using the kinematic equation: 
h = vi*t + 0.5*a*t^2, where 
h = initial height above ground (unknown)
vi = initial velocity = 10 m/s (given)
t = time taken to hit ground = 3.0 s (given)
a = acceleration due to gravity = 9.81 m/s^2
Plugging in the values: 
h = 10*3.0 + 0.5*(-9.81)*(3.0)^2 = 74.145 m
Rounding to the nearest whole number gives the answer of 74 m.

A Rock Is Thrown Downward from an Unknown Height Above