Question

Kim whirls a 10 kg bag, which is connected to a string in a
*horizontal* circle above her head at some unknown constant
speed *v*. Suddenly, the string breaks and the bag flies off
and lands 10 m away with a time of flight of 0.5 s. If the string
was 1.5 m long,

a) What was the speed of the rock before the string snapped? (vertical motion irrelevant)

b) Find the tension in the string before it snaps.

Answer #1

When the string breaks, let us assume the speed =v

since the range of flight is 10m with time of flight =0.5s

speed of the bag = distance/time = 10/0.5
=**20m/s** (because there is no acceleration in the
horizontal direction after the string breaks)

When the bag is rotated,

Forces acting on the bag are tension=T due to string and centrifugal force acting on the bag in outward radial direction.

Centrifugal force = mv^2/r where r is length of the string

so, T=mv^2/r = 10*20*20/1.5
=2666.67N=**2.67kN**

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