Work Energy And Power Question 213
Question: A cord is used to lower vertically a block of mass M, a distance d at a constant downward acceleration of $ g/4 $ . The work done by the cord on the block is
Options:
A) $ Mg\frac{d}{4} $
B) $ 3Mg\frac{d}{4} $
C) $ -3Mg\frac{d}{4} $
D) $ Mgd $
Show Answer
Answer:
Correct Answer: C
Solution:
[c] As the cord is trying to hold the motion of the block, work done by the cord is negative.
$ W=-M( g-a )d $
$ =-M( g-\frac{g}{4} )d=\frac{-3Mgd}{4} $
