Alead ball is dropped into a lake from a diving board 5m above the water . it hits the water with a certain velocity and then sink with constant velocity in bottom . it reaches the bottom 5 second after it is dropped if g= 10m/s2 . find depth of the lake and average velocity of the ball ?

1. Depth of the lake: 50 m

Explanation:

The first part of the problem can be solved by using conservation of energy.

When it is dropped, all the mechanical energy of the ball is potential energy, given by:

where m is the mass, g is the gravitational acceleration and h is the height.

When the bal hits the water, all the mechanical energy has been converted into kinetic energy:

where m is the mass and v is the speed. Equalizing the two terms, we have:

Then the ball travels in the water, keeping this constant velocity, for t=5 s. So, the total distance traveled underwater (which is the depth of the lake) is

2. Average velocity: 9.2 m/s

Explanation:

The average velocity during the whole path of the ball is equal to the ratio between the total distance traveled and the total time taken:

We already know the total distance: 5 meters above the water and 50 m underwater, so

d = 5 m + 50 m = 55 m

For the total time, we need to calculate the time spent above the water, which is given by

So the total time is: 1 second above the water + 5 seconds underwater:

t = 1 s + 5 s = 6 s

Therefore, the average velocity is

divide the right side by the left side

0.024÷1.2=0.02 for example