A force of 10 N, acting continuously, increases the kinetic energy of an object from 20.J to 60 J. Find the distance moved by the object.

Analyze the question A constant force does work on an object, and that work shows up as a change in kinetic energy. We need the distance over which the force acted.

Concept: Work-Energy Theorem Work done by the net force = change in kinetic energy

W = F × d = KE_final − KE_initial

Solution

1. Change in kinetic energy: ΔKE = 60 J − 20 J = 40 J

2. Work done equals this change: F × d = 40 J

3. Substitute F = 10 N: 10 × d = 40

4. Solve for d: d = 40 ÷ 10 = 4 m

Answer: C (4 m)

Check: Work = 10 N × 4 m = 40 J, which matches the gain in kinetic energy (60 − 20 = 40 J). ✔

Tip: In "force increases kinetic energy" questions, always subtract the initial KE from the final KE first, then divide by the force: d = ΔKE ÷ F. Don't use 60 J or 20 J alone. Using 60 ÷ 10 would give 6 m, and 20 ÷ 10 would give 2 m. Both are traps, and neither is among the options.