Question

In the figure shown, a person wants to raise a block lying on the ground to a height $h$. In both the cases if time required is same, then in which case he exerts more force? Assume pulleys to be light and frictionless, and strings to be light.

• A. (i)
• B. (ii)
• C. same in both
• D. cannot be determined

Answer 1

The correct option is A (i)

Since, $h=\frac{1}{2}a{t}^2\Rightarrow a$ should be same in both cases, because $h$ and $t$ are same in both cases as given.
In (i) $F_1-mg=ma\Rightarrow F_1=mg+ma$
In (ii) $2F_2-mg=ma\Rightarrow F_2=\frac{mg+ma}{2}$
$\therefore F_1>F_2$