7. A ball is dropped from a height of 4.0 m. Just before it hits the ground it's momentum is 8.85 kg-m/s. What is the mass of the ball?

Approximately . (Assumption: .)

Explanation:

Let the mass of this ball be .

Initial gravitational potential energy of this ball: .

Just before the ball hits the ground, all of gravitational potential energy would have been converted to kinetic energy. Calculate the velocity of the ball at that moment:

.

Therefore, right before hitting the ground, the velocity of the ball would be:

.

The momentum of an object of mass and velocity would be . Rewrite this equation to find an expression for mass given velocity and momentum :

.

Right before collision, the momentum of this ball is while its velocity is . Therefore, the mass of this ball would be:

.

c. magnitude and direction