A tower crane lifts a concrete slab weighing 2 tons to a height of 15 m. What is the work of the force of gravity acting on the slab?
m = 2 t = 2000 kg.
g = 9.8 m / s2.
h = 15 m.
The work of force A is called a scalar physical quantity, the value of which is determined by the formula: A = F * S * cosα, where F is the force that acts on the body, S is the displacement of the body, ∠α is the angle between the direction of action of the force F and displacement S.
The force of gravity F directed vertically downwards and is determined by the formula: F = m * g.
The movement of the body S directed vertically upward and in modulus is equal to the height of the lifting of the load: S = h.
since gravity is directed vertically downward and displacement is vertically upward, then ∠α = 180 °.
A = m * g * h * cosα.
A = 2000 kg * 9.8 m / s2 * 15 m * (- 1) = – 294000 J.
Answer: when lifting a load, gravity does work A = – 294000 J.
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