Question

A stone of mass 0.25 kg tied to the end of a string is whirled round in a circle of radius 1.5 m with a speed of 40 rev./min in a horizontal plane. What is the tension in the string? What is the maximum speed with which the stone can be whirled around if the string can withstand a maximum tension of 200 N?​

Answer 1

Answer:

Mass of the stone, m = 0.25 kg

Radius of the circle, r = 1.5 m

Number of revolution per second, n = 40 / 60 = 2 / 3 rps

Angular velocity, ω = v / r = 2πn

The centripetal force for the stone is provided by the tension T, in the string, i.e.,

T = FCentripetal

= mv2 / r = mrω = mr(2πn)2

= 0.25 × 1.5 × (2 × 3.14 × (2/3) )2

= 6.57 N

Maximum tension in the string, Tmax = 200 N

Tmax = mv2max / r

∴ vmax = (Tmax × r / m)1/2

= (200 × 1.5 / 0.25)1/2

= (1200)1/2 = 34.64 m/s

Therefore, the maximum speed of the stone is 34.64 m/s

Answer 2

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