Question

A boy throws a ball of mass 20g vertically upwards .It rises to max. height of 100m. At what height will K.E. be reduced to 70%

Answer 1

Answer:

h = 30 m

Concept : Conservation of energy

Explanation:

When the ball is thrown at highest point it's kinetic energy ( KE ) will be

Zero ( 0 ) that means it is converted into potential energy i.e mgH ( H = 100 m)

→ 20/1000 * 10 * 100

KE = 20 J

Now KE is reduced to 70 % that is 30 % of initial KE ( 20 J ) and it will be converted into potential energy of that height ( say h )

→ 30/100 * 20 = 20/1000 * 10 * h

→ h = 30 m