Kinetic Energy

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A body of mass 4 kg moving with a velocity of 10 m/s is brought to rest by a constant force in 5 seconds. What is the work done by the force?

RankGuru · Accepted Answer

1. **Work-Energy Theorem**: The work done by all forces acting on a particle is equal to the change in its kinetic energy ($W = \Delta K$).
2. **Initial Kinetic Energy ($K_i$)**:
   - $K_i = \frac{1}{2} m v^2 = \frac{1}{2} 	imes 4 	imes (10)^2 = 2 	imes 100 = 200$ J.
3. **Final Kinetic Energy ($K_f$)**:
   - Since it is brought to rest, $K_f = 0$ J.
4. **Work Calculation**:
   - $W = K_f - K_i = 0 - 200 = -200$ J.
5. **Interpretation**: The negative sign indicates that the force is doing work in a direction opposite to the displacement (resistive force).

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