Worksheet: Rotational Equilibrium

In this worksheet, we will practice calculating the positions and masses of objects in rotational systems such that the net rotational acceleration is zero.

Q1:

A uniform seesaw is balanced on a fulcrum located 3.0 m from the left end, as shown. The smaller boy on the right has a mass of 40 kg and the bigger boy on the left has a mass 80 kg. What is the mass of the board?

Q2:

The uniform seesaw is balanced at its centre of mass, as shown. The smaller boy on the right has a mass of 40 kg. What is the mass of his friend?

  • A 83 kg
  • B 78 kg
  • C 85 kg
  • D 80 kg
  • E 88 kg

Q3:

A uniform 40.0-kg scaffold of length 6.0 m is supported by two light cables, as shown in the figure. An 80.0-kg painter stands 1.0 m from the left end of the scaffold, and his painting equipment is 1.5 m from the right end. The tension in the left cable is twice that in the right cable.

Find the tension in the right cable.

Find the tension in the left cable.

Find the mass of the equipment.

Q4:

The forearm shown in the diagram is positioned at an angle 𝜃 with respect to the upper arm, and a ball with a mass of 5.0 kg is held in the hand. The total mass of the forearm and hand is 3.0 kg, and their center of mass is 15.0 cm from the elbow.