Question

A box of mass 8.0 kg is lifted from the ground and placed on a shelf. The box gains 100J of potential energy.

The box falls off the shelf . Air resistance can be ignored. At what speed does the ball hit the ground.

Answer 1

Explanation:

If h be the required height , the potential energy PE=mgh

or h=PE/mg=5.8×10145=2.5m

Answer 2

Given :

Mass (m) = 8 Kg

Potential Energy (PE) = 100 J

To Find :

At what speed does the ball hit the ground.

Solution :

When the ball falls from the shelf its potential energy gets converted into kinetic energy.

Let 'm' be the mass, 'h' be the height of the shelf, ''v' be the speed of the ball.

So,

Potential energy of the ball = Kinetic Energy energy of the ball

⇒    mgh                                 =   $\frac{1}{2} mv^2$

⇒    100                                  =   $\frac{1}{2} *8 * v^2$

⇒       v                                   = $\sqrt{\frac{200}{8} }$

∴        v                                   = 5 m/sec

Therefore, the speed of the ball is found to be 5 m/sec.