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:

.

r=rho l/a where a is the area, l is the length and rho is resistivity so the greater the area the lesser the resistance thats why the earth pin is thicker bcos current follow the shortest path, so less resistive .

the answer is b ) square root of 5