Question

A 2-kg mass hangs above a table on a 1-m string. The mass just clears the table. Use the idea of conservation of energy to describe how the pendulum can be used to move a 1-kg book across the table.

Answer 1

One way to use the pendulum to move a 1-kg book across the table is through the transfer of energy from potential energy to kinetic energy.

When the mass is lifted and released, it swings back and forth as a pendulum. At the highest point in its swing, the mass has maximum potential energy and minimum kinetic energy. As the mass moves down towards the bottom of its swing, potential energy is converted into kinetic energy.

If a 1-kg book is placed on the table directly below the path of the swinging mass, the mass can be timed to swing at the right moment to hit the book with sufficient force to slide it across the table. This occurs when the mass is at its lowest point in its swing, where it has maximum kinetic energy and minimum potential energy.

The kinetic energy of the swinging mass is transferred to the book upon impact, causing it to move across the table. If the timing of the swing is just right, the book will continue moving until it reaches the other end of the table. The height of the pendulum's swing can be adjusted to control the speed and distance that the book travels.