The work–energy theorem states that the work done by the net force acting on a body is equal to the change in its kinetic energy.
Work done by the resultant force on a body is equal to the change in kinetic energy of the body.
Work done (W) = Change in kinetic energy
W = KEfinal − KEinitial
W = (1/2) m v2 − (1/2) m u2
If work done on a body is positive, its kinetic energy increases. If work done is negative, its kinetic energy decreases.
Q1. Work–energy theorem relates: A) Force and velocity B) Work and energy C) Force and momentum D) Power and energy Answer: B Q2. According to work–energy theorem, work done is equal to: A) Final kinetic energy B) Initial kinetic energy C) Change in kinetic energy D) Momentum change Answer: C Q3. Formula for work–energy theorem is: A) W = F × s B) W = mgh C) W = (1/2) m v² D) W = (1/2) m v² − (1/2) m u² Answer: D Q4. If work done is negative, the kinetic energy of a body: A) Increases B) Decreases C) Remains constant D) Becomes zero Answer: B Q5. A body of mass 2 kg moves from rest to velocity 4 m/s. Find the work done. A) 8 J B) 16 J C) 32 J D) 64 J Answer: C Q6. Brakes applied to a moving vehicle result in: A) Increase in kinetic energy B) Decrease in kinetic energy C) No change in kinetic energy D) Maximum kinetic energy Answer: B Q7. Work–energy theorem is applicable to: A) Only stationary bodies B) Only moving bodies C) Both stationary and moving bodies D) Only free-falling bodies Answer: C Q8. If initial and final kinetic energies are equal, work done is: A) Positive B) Negative C) Zero D) Infinite Answer: C
Work done by the net force on a body is equal to the change in its kinetic energy.
W = KEfinal − KEinitial
W = (1/2) m v2 − (1/2) m u2
Numericals are frequently asked using work–energy theorem. Always calculate change in kinetic energy carefully.
