Question

In the the given figure, 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 has to exert more force? (Assume pulleys and strings are massless and pulleys are smooth).

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

Answer 1

Answer: (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) $2F_2-mg=ma$

$\Rightarrow F_2=\frac{mg+ma}{2}$

$\therefore F_1>F_2.$
Answer is A