# For a body moving from position Xa to position Xb under a variable force, what is the work done?

Category: QuestionsFor a body moving from position Xa to position Xb under a variable force, what is the work done?
Editor">Editor Staff asked 1 year ago

For a body moving from position Xa to position Xb under a variable force, what is the work done?

(a) W = F * (X2 – X1)

(b) -W = F * (X2 – X1)

(c) W = -F * (X2 – X1)

(d) W = F * (X1 – X2)

This question was posed to me during an interview.

The origin of the question is Work-Energy Theorem for a Variable Force topic in division Work, Energy and Power of Physics – Class 11
Select the correct answer from above options
Interview Questions and Answers, Database Interview Questions and Answers for Freshers and Experience

Editor">Editor Staff answered 1 year ago

The correct choice is (a) W = F * (X2 – X1)

The explanation is: Kinetic energy (K) = 1/2 x m x v^2

dK/dt = m*v*dv/dt

Force (F) = m*a

= m*dv/dt

dK/dt = F*v

= m*v*dv/dt

K2
K1
dK/dt =

Xb
Xa
F * dX/dt

K2
K1
dK =

Xb
Xa
F * dX

K2 – K1 = F (X2 – X1)

W = F * (X2 – X1).

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