Question

A person holds a weight of 10 kg at a height of 5 m above the ground for 5
minutes. Work done by him is
(a) Zero (b) 50 J (c) 250 J (d) 300 J​

Answer 1

Explanation:

Answer : option (a) zero

explanation : workdone is the dot product of force applied on body and displacement of body due to applied force.

i.e., W=\vec{F}.\vec{S}W=

F

.

S

here in question, A person holds on a weight of 10kg at a height of 5m above the ground.

so, force applied on body by person , F = weight of body = mg = 10 × 10 = 100N

person doesn't move from his position. so, displacement of person , S = 0

hence, workdone = 100. 0 = 0

hence , workdone by person on the object equals zero.

Answer 2

Given: A person holds a weight of 10 kg at a height of 5 m above the ground for 5 minutes.

To find: Work done by him.

Solution:

• Work done is the product of the force applied on the weight and the displacement of the weight.

        $W = F.d$

• In this case, force applied on the weight is the product of the mass and the acceleration due to gravity.

       $F = mg$

       $F = 10kg * 10ms^{-2}$

           $= 100N$

• Now, we use the work done formula.
• But the displacement of the weight is zero as it is mentioned in the question that the persons 'holds' the weight.
• So,

       $F = 100N * 0$

           $= 0 J$

Therefore, work done by him is zero.