In each of the following a force, $F$ is acting on an object of mass $M$ . The direction of displacement is from west to east shown by the longer arrow. Observe the diagram carefully and state whether the work done by the force is negative, positive, or zero.

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Solution

Workdone $W = \to F . \to S = F S$ $c o s θ$ where $θ$ is the angle between $\to F$ and $\to S$
For (a) : $θ = 90^{\circ}$
$∴$ $W = F S$ $c o s 90^{\circ} = 0$

For (b) : $θ = 0^{\circ}$
$∴$ $W = F S$ $c o s 0^{\circ} = F S > 0$

For (c) : $θ = 180^{\circ}$
$∴$ $W = F S$ $c o s 180^{\circ} = - F S < 0$

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In each of the following a force, F is acting on an object of mass M. The direction of displacement is from west to east shown by the longer arrow. Observe the diagram carefully and state whether the work done by the force is negative, positive, or zero.

Workdone W=→F.→S=FS cosθ where θ is the angle between →F and →SFor (a) : θ=90∘ ∴ W=FS cos90∘=0 For (b) : θ=0∘ ∴ W=FS cos0∘=FS>0 For (c) : θ=180∘ ∴ W=FS cos180∘=−FS<0

In each of the following a force, $F$ is acting on an object of mass $M$ . The direction of displacement is from west to east shown by the longer arrow. Observe the diagram carefully and state whether the work done by the force is negative, positive, or zero.