A spherical body of mass 2 kg starting from rest acquires a kinetic energy of 10000 J at the end of 5ᵗʰ second. The force acted on the body is ________ N.

Solution

Physics sir · 3 steps

Get the speed from the kinetic energy first, then the force is just mass times the rate of change of speed.

1. Speed from KE. Use K = 1/2mv² with m = 2 kg and K = 10000 J. This gives 10000 = 1/2 × 2 × v², so v² = 10000 and v = 100 m s⁻¹.
2. Find acceleration. The body starts from rest and a constant force gives a constant acceleration. It reaches 100 m s⁻¹ in 5 s, so a = (100 - 0)/5 = 20 m s⁻².

   F = ma = 2 × 20 = 40 N

3. So. The force acting on the body is 40 N.

The idea to keep. When energy and time are given, turn the energy into a speed first. From speed and time you get acceleration, and F = ma finishes the job.

Answer from the NTA final answer key. Solution by PrepWiser.