Problem 55.

A coin is dropped from a 400 m high tower. What is the coin's velocity when it hits the ground? How long does it take to get there?

Solution:

This is the free fall motion – motion with constant acceleration, . The equations, which describe this motion, are the following:

where the axis y has upward direction.

The final position of the coin is the ground. The coordinate of the final point is -400m. We can substitute this value in the first equation and obtain the traveled time:

Then

Then from the second equation we can find the velocity of the coin at the ground:

The minus sign means that the direction of velocity is downward.