Question #a5d68

1 Answer
Mar 17, 2016

Answer:

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.