physics

PHYSICS- ABOUT ENERGY

I have a couple of questions for you. I know the answer but not how you get to the answer. Yani javabesho daram monta shejoori hesab va halesh mikoni nemidanam.

Question 1

A tennis ball (mass 70 kg) is dropped from the height 2.5 meters.

a) How big kinetic energy (Ek=mv^2/2) does the ball have immediately before it hits the floor?

The answer is: 1.7 J

After a bounce against the floor the ball reach the height 1.5 meter.

b) What kinetic energy does the ball have just before it leave the floor?

The answe is: 1.0 J


Question 2

A stone is dropped from 20 meter over the ground. What speed have it...

a) at the stroke

The answer is: 19,8 m/s

b) in the halfway

The answer is: 14.0 m/s


Question 3

A box or "cardboard" with history books with the mass 30 kg starts to glide down from a board with insignificant friction. When it glides 2.5 meters the speed is 5.0 m/s.

a) How big power have seem along the board.

The answer is: 0.15 kN

b) Calculate the force of gravity work.

The answer is: 0.38 kJ

c) How big is the box vertical move h?

The answer is: 1.3 meter