Option (D) is the correct one.
In order to increase the amount of work done, we need to increase the force applied to the object.
Answer:
40 N
Explanation:
We are given that
Speed of system is constant
Therefore, acceleration=a=0
Tension applied on block B=T=50 N
Friction force=f=10 N
We have to find the friction force acting on block A.
Let T' be the tension in string connecting block A and block B and friction force on block A be f'.
For Block B

Where
=Mass of block B
Substitute the values


For block A

Where
Mass of block A
Substitute the values


Hence, the friction force acting on block A=40 N
The answer is D
<em>"</em><em>a property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force.</em><em>"</em>