Question

A string tied on a roof can bear a maximum weight of 50 kg wt. The minimum acceleration that can be acquired by a man of 98 kg to descend will be :
(take g=$9.8m/s^2$.

• A. $9.8m/s^2$.
• B. 4.9 $m/s^2$.
• C. 4.8$m/s^2$.
• D. 5$m/s^2$.

Answer 1

The correct option is C 4.8$m/s^2$.

The correct answer is C.

Given,

The weight of roof is $50kg$

The weight of man is $98kg$

Let T be the Tension in the string.

Let the acceleration of the descending man be a. It is the weight of the person which gives acceleration to the person. But tension opposes the weight.

$mg-T=ma$

$T=m(g-a)$

$a=g-\frac{T}{m}$

Given the maximum tension T, so we get the minimum acceleration. So the person must descend with more acceleration than this.

$a=g-\frac{50\times g}{98}=4.8m/sec²$ g = 9.8 m/s²$