Answer to Question #269781 in Mechanics | Relativity for efe

Question

A 70 kg

kg petty thief wants to escape from a third-story jail window. Unfortunately, a makeshift rope made of sheets tied together can support a mass of only 64 kg

kg 

Give a quantitative answer.?

Answer 1

If it can support a mass of $64kg$ , the breaking force is the weight of $64kg$ or $64kg×9.80N/kg = 627.2N.$ This would be the maximum upward force the sheets could supply.

Mr. thief could accelerate downward at a constant rate, thereby reducing the tension in the sheets to this value. So the thief would have $627.2N$ of force upward (+), and his own weight $70kg×9.80N/kg =686N$ down (-) and our$F=ma$ :

$\frac{627.2N-686N}{70} =-0.84m/s^2$

$a =-0.84m/s^2$ . By accelerating downwards at $0.84m/s^2$