When you drop a pebble from height H, it reaches the ground with speed V if there is no air resistance. From what height should you drop it so it will reach the ground with twice speed?
A) 2H
B) 8H
C) 5H
D) 16H
E) 4H

Question

Quizplus · Accepted Answer

The speed of the pebble is proportional to the square root of the height (V = sqrt(2gH)). To double the speed, the height must be quadrupled (4H) because (sqrt(4) = 2).

When You Drop a Pebble from Height H, It Reaches