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: d. a cme increases the amount of energy in the solar wind

explanation:

coronal mass ejections, also called cmes, are large clouds of plasma and magnetic field that erupt from the sun. only when the cloud is aimed at earth will the cme hit earth and therefore cause impacts. high-speed solar wind streams come from areas on the sun known as coronal holes.

the part of the wave he is travelling on is the crest