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The gravitational potential difference between a point on a planet's surface and another point 10 m vertically above it is 4 J/kg. Treating the gravitational field as uniform, how much work is done in moving a 2.0 kg mass from the surface to a point 5.0 m above the surface?

1. 0.40 J
2. 2.5 J
3. 4.0 J
4. 8.0 J

Correct answer: 4.0 J

Solution

Uniform field means potential difference is proportional to height. The potential difference over 5 m is half that over 10 m (i.e., 2 J/kg). Work done = mass times this potential difference.

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