Exit Ticket Lecture 8 Rotational Kinetic Energy

A ball and a block of ice with the same mass are released from rest at the top of two identical ramps. The ball rolls without slipping, and the ice block slides down the ramp with no friction.

• The sliding ice block reaches the ground last.

• The rolling ball reaches the ground last.

• It depends on the size of the ball.

• Both objects reach the ground at the same time.

Answer explanation

Before the objects are released, they only have potential energy. They have the same mass and are released from the same height, so they have the same initial potential energy.

When the objects reach the ground, all of their potential energy has been converted into kinetic energy.

The rolling ball has both translational and rotational kinetic energy. The sliding ice block only has translational kinetic energy.

Since the rolling ball has to convert the potential energy into two kinds of kinetic energy, it will have a lower final linear speed and reach the ground last.

Two disks with the same mass and radius are released from rest at the top of two identical ramps. One disk rolls without slipping, and one slides down the ramp with no friction.

• The rolling ball reaches the ground last.

• It depends on the size of the ball.

• Both objects reach the ground at the same time.

• The sliding disc reaches the ground last.

Answer explanation

Before the objects are released, they only have potential energy. They have the same mass and are released from the same height, so they have the same initial potential energy.

When the objects reach the ground, all of their potential energy has been converted into kinetic energy.

The rolling ball has both translational and rotational kinetic energy. The sliding disc only has translational kinetic energy.Since the rolling ball has to convert the potential energy into two kinds of kinetic energy, it will have a lower final linear speed and reach the ground last.