Question

A woman drops a rock from a bridge to the water 17.5 m below. with what speed does the rock strike the water?

a. 0 m/s
b. 18.5 m/s
c. 171m/s
d. 9.8 m/s
e. 17.5 m/s

Answer 1

Given :

Height from which rock is dropped, h = 17.5 m.

Initial velocity, u = 0 m/s.

To Find :

Speed does the rock strike the water.

Solution :

We know, by equation of motion :

`v^2-u^2=2as` ......( 1 )

Here , a = g = 9.8 m/s² ( Acceleration due to gravity )

Putting all given values in 1 , we get :

`v^2-u^2=2as\\\\v=√(2gh)\\\\v=√(2* 9.8* 17.5)\ m/s\\\\v=18.5\ m/s`

Therefore, speed with rock strike the water is 18.5 m/s.

Hence, this is the required solution.