Question

A cord is used to lower vertically a block of mass M, through a distance d at a constant downward acceleration of g/4

​
. Then the work done by the cord on the block is​

Answer 1

Explanation:

Mg−T=Ma=M(

8

g

)

⇒T=M(g−

8

g

)=

8

7

Mg

Work done by the cord : W=T×dcos180

∘

=

8

7

Mgd(−1)=−7Mgd/8

Answer 2

Answer:

The work done by the cord on the block is - 3 Mg d/4.

Explanation:

Given: Mass = M

  displacement = d

  downward acceleration g/4.

To find: Work done by the cord.

Solution: Through the concept of #Pseudo Force, we know that:

              Tension, T = m (g-a)

For the above case:

                    T = M ( g - g /4)

                   T = 3 Mg/4

#For work done, we know that:

                   W = F s cos∅

                   W = 3 Mg/4 × d × cos 180°

[∵ T = F = 3 Mg/4 and ∅ = 180° for the cord is descending straightly]

                   W = - 3 Mg d/4

Hence, the work done by the cord on the block is - 3 Mg d/4.