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?

H quadrupled

Explanation:

Since we are neglecting air resistant, gravitational acceleration g is the only thing that affect the pebble:

As v = gt. To get twice the speed 2v with the same acceleration g, the time must be doubled.

Yet to get to distance H with 2t time. Since . If t is doubled, H must be times the original amount.

answer; how far out of place which the object finished relative to the starting location;