Example 1 · level 1
Joseph pulls a suitcase 7 m along the floor with a force of 25 N applied at 0° to the horizontal. Find the work done by this force (in J).
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- W = 25 × 7 × 1 = 175 J.
Answer: 175 J
CLASS 11–12 PHYSICS · WORK, ENERGY AND POWER
Work–energy theorem and spring energy
Net work done = change in kinetic energy: W = ½mv² − ½mu². Work by a force at angle θ: W = Fs cosθ. Spring potential energy U = ½kx².
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Worked examples
Example 2 · level 2
A net constant force acts on a 4 kg body over a distance of 10 m, increasing its speed from 0 m/s to 8 m/s. Using the work–energy theorem, find the force (in N, correct to 2 decimal places).
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- ΔKE = 128 J.
- F = ΔKE ÷ s = 128 ÷ 10 = 12.8 N.
Answer: 12.8 N
Example 3 · level 3
A spring of force constant 500 N/m in a toy launcher is compressed by 2 cm. How much elastic potential energy is stored (in J, correct to 2 decimal places)?
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- U = ½ × 500 × 0.02² = 0.1 J.
Answer: 0.1 J