# A small object, of mass 0·02kg at the top of a building 160 m high, is dropped from rest. (a) Ignoring air resistance, calculate the speed of the object as it hits the ground and the time taken...

A small object, of mass 0·02kg at the top of a building 160 m high, is dropped from rest.

*(a) *Ignoring air resistance, calculate

- the speed of the object as it hits the ground and the time taken for the object to reach the ground.

*print*Print*list*Cite

### 1 Answer

We can use the equations of motion here.

`darrV^2 = U^2+2aS`

`V = ?`

`U = 0` as it is dropped.

`a = 9.81m/s^2`

`S = 160m`

`V^2 = 0+2xx9.81xx160`

`V^2 = 3139.2`

`V = 56.03m/s`

Using `darrV = U+at`

`t = (V-U)/a`

`t = (56.03-0)/9.81`

`t = 5.71s`

**So when the ball hit the ground the velocity will be 56.03 and 5.71 seconds will be the time taken.**

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