First slide

Work

Question

A ball of mass 100g is projected upward with an initial velocity $10 m s^{- 1}$ and comes back and finally achieved a velocity of $5 m s^{- 1}$ at the point of projection. The work done by air resistance

Moderate

A

3.75 J
B

0.375J
C

-3.75 J
D

-0.375 J

Solution

$\begin{array}{l} W = ΔK . E \\ W_{g} + W_{air} = {KE}_{f} - {KE}_{i} \\ 0 + W_{air} = \frac{1}{2} \times 100 \times 10^{- 3} [5^{2} - 10^{2}] \\ W_{air} = \frac{1}{2} \times 10^{- 1} \times - 75 \\ = - 3.75 J \end{array}$

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