Example 1 · level 1
Arjun pushes a cart with a force of 60 N through 20 m in the direction of the force. Find the work done (in J).
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- W = 60 × 20 = 1,200 J.
Answer: 1,200 J
CLASS 9 SCIENCE · WORK AND ENERGY
Work done by a force
Work = force × displacement in the direction of the force (W = Fs), in joules. Lifting a load: W = mgh.
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Worked examples
Example 2 · level 2
A porter at Nagpur station lifts a 39 kg suitcase through a height of 5 m. Find the work done against gravity (in J). Take g = 10 m/s².
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- W = 39 × 10 × 5 = 1,950 J.
Answer: 1,950 J
Example 3 · level 3
A crane does 80 J of work lifting a 4 kg load straight up at steady speed. Through what height (in m) was it lifted? Take g = 10 m/s².
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- h = 80 ÷ 40 = 2 m.
Answer: 2 m