The work of the force is equal to the product of the modulus of this force by the modulus of displacement of the body and by the cosine of the angle between the directions of force and displacement.
The force of gravity F = mg, where m is the mass of the body and g is the acceleration of gravity, acts against displacement, therefore cosa = –1. Then the work of gravity will be A = -1 kg • 10 m / s2 • (3-1) m = – 20 J.
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