Answer:
Removing some of the books reduced the mass of the box, and less force was needed to push it across the floor.
Average speed is defined as the ratio of total distance covered in total given time

here we know that total distance that man moved is


so total distance is



now here total time of the motion is


total time will be given as


now by above formula


so his average speed is 30 km/h
It is wasted, most likely as light, in this case, or it is lost during the transport of electricity.
Answer:
Gravitational potential energy is energy an object possesses because of its position in a gravitational field. Since the force required to lift it is equal to its weight, it follows that the gravitational potential energy is equal to its weight times the height to which it is lifted.
It does not move because of the sun the sun has no energy.