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Question

What force (effort) will be required to push a load, initially at rest, of mass 500 g, so that at a distance of 20 m, its final velocity is 20 m/sec [Assume that there is no friction and 'g' = 10 m/s²].

This question was previously asked in
RRB NTPC 2024 Undergraduate CBT 1 Question Paper (29-Aug-2025) (Shift 1)
The correct answer is

5 N

This problem involves applying the principles of Newtonian mechanics, specifically the work-energy theorem. Since there's no friction, the work done on the object is equal to its change in kinetic energy.

1. Calculate the change in kinetic energy:

The initial kinetic energy is zero because the object is initially at rest. The final kinetic energy is given by:

\(KE_f = \frac{1}{2}mv^2\)

where:

  • \(m\) = mass = 500 g = 0.5 kg
  • \(v\) = final velocity = 20 m/s

Substituting the values:

\(KE_f = \frac{1}{2}(0.5 kg)(20 m/s)^2 = 100 J\)

2. Calculate the work done:

The work-energy theorem states that the work done on an object is equal to its change in kinetic energy. Therefore, the work done is 100 J.

3. Calculate the force:

Work is defined as the product of force and displacement:

\(W = Fd\)

where:

  • \(W\) = work done = 100 J
  • \(F\) = force (effort)
  • \(d\) = displacement = 20 m

Solving for \(F\):

\(F = \frac{W}{d} = \frac{100 J}{20 m} = 5 N\)

Therefore, the force required is 5 N.

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