Question

A block of mass 10 Kg accelerates from rest to a velocity of 20 m/s in 5s under the influence of an external force. What is the work done by the external force?

(a) 2000 J

(b) -2000 J

(c) 20000 J

(d) -20000 J

I have been asked this question by my school principal while I was bunking the class.

Question is taken from Work topic in chapter Work, Energy and Power of Physics – Class 11

Answer 1

The correct answer is (a) 2000 J

To elaborate: The acceleration can be found out by using the initial and final velocities and the time taken. Acceleration = 4 m/s^2. Force can be found out by the second law. By the second equation of motion the distance covered in 5 s can be found which is equal to 50 m. Work can be found out by multiplying the force and the distance covered. Work = 2000 J.