When you drop a pebble from height H, it reaches the ground with kinetic energy K if there is no air resistance. From what height should you drop it so it will reach the ground with twice as much
Kinetic energy?
A) 4H
B) 8H
C) $\sqrt { 2 H }$
D) 16H
E) 2H

Question

When you drop a pebble from height H, it reaches the ground with kinetic energy K if there is no air resistance. From what height should you drop it so it will reach the ground with twice as much
Kinetic energy? 
A)  4H 
B)  8H 
C) $\sqrt { 2 H }$
D)  16H
E)  2H

Quizplus · Accepted Answer

The kinetic energy of the pebble is proportional to the height from which it is dropped. To double the kinetic energy, you need to double the height, so the new height should be 2H.

When You Drop a Pebble from Height H, It Reaches 2H\sqrt { 2 H }2H​

When You Drop a Pebble from Height H, It Reaches $\sqrt { 2 H }$