Question

Lab 8 Individual Wrap Up

Wrap up question 1: Is the tennis ball catch more similar to the happy ball or the sad ball? Explain your answer using the energies in each scenario.

Wrap up question 2: Describe the resulting behavior of a tennis ball if a force momentarily did positive work on the ball, then a smaller force consistently did negative work on the ball, as the ball moved downwards through the air. Be specific about changes to the total energy, the kinetic energy, and the potential energy of the ball.

Wrap up question 3: If the mass on the hanging spring is pulled down and released, it starts to bounce. Do you expect the distance the mass bounces each time will stay the same, increase, or decrease? Explain using work and energy.

Answer 1

1. No, tennis ball catch is not similar to happy or sad ball catch. Here in the tennis ball, the mass is heavier and so is the air resistance. thus, the ball falls down with much greater thrust than the happy ball. The happy ball weighs negligible compared to the tennis ball. Thus, in order to catch the tennis ball, we need to increase the time of flight so as to reduce the pain. but in the happy ball, this doesn't happen.

in terms of energy: PE = mgh

so tennis ball of mass 0.05 Kg dropped from height 2 m

PE = 1 N

this is converted to kinetic energy when the ball falls down.

PE for the happy ball is << 1 N.

2. force does positive work on the ball: Here let's assume the ball is coming down with KE = 1 N. now if the ball is struck with a racquet. then the bat does positive work on the ball and the ball changes its direction. after some time, the ball again comes down and negative work is done.

Here to conserve energy during a collision, the energy is released in the form of heat or sound. Now, the ball's energy increases since the kinetic energy of the racquet add with the kinetic energy of the ball.

3. when a mass is attached to spring, it bounces when given a force. this distance remains unless any external force acts. Here the total energy of the system remains constant. that is when the spring is fully stretched/ compressed, the kinetic energy is zero. so total energy is equal to elastic/potential energy. at the equilibrium position, the elastic energy is zero, the total energy is equal to the kinetic energy. thus, on the whole, the total energy is always conserved.