Question

A 30 kg child sits on a seesaw at a distance of 2 m from the fulcrum. Where must the child's parent sit to balance the seesaw if the parent has a mass of 90 kg?

A. 67 cm from the child
B. 67 cm from the fulcrum
C. 133 cm from the child
D. 267 cm from the fulcrum

Answer 1

The parent must sit 67 cm from the fulcrum to balance the seesaw. This is determined by using the principle of moments where the product of the child's weight and distance from the pivot must equal the product of the parent's weight and distance to achieve equilibrium.

Step-by-step explanation:

To find out where the child's parent must sit to balance the seesaw, we can use the principle of moments. The principle of moments states that for the seesaw to be in equilibrium, the clockwise moments must equal the anticlockwise moments about the pivot. The moment is calculated as the product of the force exerted (due to the weight of the person) and the distance from the pivot point.

For the child, the moment is 30 kg × 2 m = 60 kg·m. The parent is heavier and must therefore sit closer to the fulcrum to balance the seesaw. To find the exact distance, we divide the child's moment by the parent's weight. The parent's moment must be 60 kg·m to balance the seesaw, so the distance from the fulcrum (d) for the parent's weight (90 kg) is calculated by the equation 60 kg·m = 90 kg × d, which gives us d = 60 kg·m / 90 kg = 0.67 m or 67 cm from the fulcrum.

Therefore, the correct answer is B. 67 cm from the fulcrum.