Question

Question #a5d68

Answer 1

C

Explanation:

Work done `=vecFcdot vecx`,
When force `vecF` moves through a distance `vecx`

It is true that physically distance moved by weight is along the direction of `vecr`. The weight `W` is due to force of gravity and is acting in the downwards direction.

From the picture `vecr` can be resolved into its `x and y` components,
`vecr=vecp+vecq`
Work done `=-vecWcdotvecr=-vecWcdot(vecp+vecq)`
we know that in a dot product for `theta=90^@`, `cos theta=0`. Therefore, first part `vecWcdot vecp=0`
We obtain work done `=-vecWcdotvecq=-|vecW|cdot|vecq|costheta`
Angle between the two is `180^@ and cos 180^@=-1`
Hence the result.