Question

You drop a block (5.47 kg) from a height of 21.61 m onto spring (k = 93.2 N/m). The spring compresses and then relaunches the ball. We will assume that air drag acts as a constant external force when the ball is travelling in the air. F(drag) = 2.7 N

What is the work done by external forces when the block falls to the ground ?

Answer 1

We are assuming here the situation since ball drop to reach the ground only.

First, We can see that work done by spring force should be Zero because Spring came back in its natural length.

Now we will calculate the time took by the ball to reach the ground, is-

S = ut + (0.5)at²

21.61 = 0 + 0.5*10*t²

t = 2.08 sec

Now We will calculate the Work done by external forces-

Wexternal = W(mg) + W(Fdag)

Wexternal = F(mg)t + F(dag)t (F(dag) should be consider with -ve sign because its a dragging Force and applied in opposite direction of motion)

Wexternal = 5.47*10*(2.08) - 2.7(2.08)

Wexternal = 113.776 - 5.616

Wexternal = 108.16 J

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