Question

When a certain 25.0g rubber ball is dropped from a height of 1.25 meters onto a hard surface, the ball loses 185 of its potential + kinetic energies. Using algebraic-based physics:

a) What energy did the ball have just after bouncing off the floor (on its way back up to 1.25 m)?

b) What energy did the ball have just before hitting the floor?

c) If you throw the ball down, still releasing the ball at 1.25 m, how fast does the ball need to be moving when you let go of it so that the ball will bounce back up to 1.25 m?

Answer 1

mass of ball (m) = 0.025 Kg

height (h) = 1.25 m

Initial potential energy of ball = mgh = 0.025*1.25*9.81 = 0.3065625 J = 306.5625 mJ

Energy lost on hitting floor = 185 mJ

a) Energy left on bouncing= 306.5625-185 = 121.5625 mJ

b) Just before hitting the wall , energy in ball = initial energy = initial Potential Energy = 306.5625 mJ

c) For the ball to bounce back to 1.25 m, KE of ball after hitting = PE at highest point

(1/2) m v² + mgh - 185= 306.5625

=> (1/2) m v² = 185 => v = 3.847 m/s