Question

A father holds his child on his shoulders during a parade. The father does no work during the parade because:

• A. No force acts on the child
• B. The momentum of the child is constant
• C. The potential energy of the child is varying
• D. The child's kinetic energy is constant
• E. The child's distance from the ground remains the same

Answer 1

Answer: (E)

The child's distance from the ground remains the same

We know , work is given by ,

$W=fdcos\theta$

In the given example, father exerts force on child in upward direction and his displacement is in forward direction , therefore angle between force and displacement is ${90}^o$ due to this work done is zero. Also there is no upward or downward displacement of child is taking place as work done is zero. Hence child's distance from the ground remains the same.