Two blocks of masses 5 kg and 10 kg are connected by a metal wire going over a smooth pulley as shown in the figure. The breaking stress of the metal wire is 2 × 10 ^ 9 Nm^ - 2 . If g = 10ms^ - 2 ,& then what is the

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Correct answer: A. 0.1mm

This is Atwood's machine. Let the tension in the wire be

T

and acceleration of masses

a

.

Then,

T - 5g = 5a

and

10g - T = 10a

This gives

a = \dfrac{1}{3}g

and

T = \dfrac{20}{3}\text{g} = \dfrac{200}{3}\text{N}

.

Stress

= \dfrac{T }{area} = \dfrac{200}{3 \times 3\text{.}14 \times r{}^{2}} = 2 \times {10}^{9}\text{(given)}

Thus the minimum radius

r

should be

r = \sqrt{\dfrac{200}{3 \times 3\text{.}14 \times 2 \times {10}^{9}}} = 1\text{.}03 \times {10}^{- 4}m \approx 0\text{.}1\text{mm}

Two blocks of masses 5 kg and 10 kg are connected by a metal wire...

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