# Homework Help: Ball dropped into lake.

1. Jan 30, 2010

### maxwellsmooth

1. The problem statement, all variables and given/known data

A lead ball is dropped into a lake from a diving board 5.0 meters above the water. After entering the water, it sinks to the bottom with a constant velocity equal to the velocity with which it hit the water. The ball reaches the bottom 3.0 seconds after it is released. How deep is the lake?

3. The attempt at a solution

I am not sure how to begin this problem. Any help would be appreciated.

2. Jan 30, 2010

### AEM

Start out by finding the velocity of the ball as it hits the water. Assume that the ball starts from rest when dropped from the diving board and use an equation that involves the acceleration due to gravity, the velocity of the ball, and the distance from the diving board to the water.

Once you have the velocity of the ball in the water it should be a simple matter to calculate the depth of the water using an equation that relates distance traveled to the velocity and the time taken.

3. Feb 2, 2010

### maxwellsmooth

Thank you.

This is what I came up witjh:

d= (1/2)*9.8m/s^2*t^2

5 m = 1/2*9.8m/s^2*t^2

t = 1 sec

So it takes 1 sec for the ball to hit the water. The velocity is 5 m/s.

Since there are 2 seconds left for it to reach the bottom of the lake the lake is 10 meters deep.

Thank you.