Question

1. A piece of rock is thrown into a pile of sand. How is energy conserved in this case?
a Kinetic energy at the maximum height is converted to potential energy and when it touches the ground, it changes partially to work and heat.
b. Potential energy at the maximum height is converted to translational kinetic energy and when it touches the ground, it is lost.
c. Potential energy at the maximum height is converted to translational kinetic energy and when it touches the ground, it changes to work and heat.
d. Kinetic energy at the maximum height is converted to potential energy and when it touches the ground, it is lost.

2. A boy stretches a rubberband and lets it fly across the room. When does the rubber band have energy?
a. The instant the band is stretched from its state of rest.
b. Only when its flying across the room.
c. Only when it was stretched tight.
d. Both when its stretched tight and when its flying across the room.

Please explain the concept behind this question and prove why the incorrect options are not valid.

Answer 1

1) option c  Potential energy at the maximum height is converted to translational kinetic energy and when it touches the ground, it changes to work and heat.when rock is at height it has potential energy when it moving downwards it is having kinetic energy once it lands on sand it get resistance and energy is transformed into work

2)when the rubber band is stretched work done is stored in form of elastic potential energy ,and when it is moving it has kinetic energy so both has energy option d