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# M3 springs/strings watch

1. Recently started out on springs, few problems, help greatly appreciated

1) Particle of mass 3kg is attached to one end of a light elastic string, natural length is 1m, modulus of elasticity is 14.7N. The other end of the string is attached to a fixed point. Particle is held in equilibrium by a horizontal force of 9.8N, string inclined to verticle at an angle x.
a) value of x
b) extension of string
c) If the horizontal force is removed, find the magnitude of the least force that will keep the string inclined at the same angle?

I have worked through a and b, however I am not sure how to approach part c. Here are my workings of a and b... ( I have also attached a diagram)

a) 9.8 = sin x T and T cos x = 3g, therefore tan x = 1/3
b) choosing 9.8 = sin x T, T = 9.8/sin x.
Setting T = 14.7s/1 gives s = 2.11 ( where s is the extension in the string)
Attached Images

2. (Original post by rainbowsss)
...
Hints:

Triangle of forces.

You know one force (3g)

You know the direction of the tension.

Draw a diagram - you need this!

What's the third force that creates equilibrium, and when will it be a minimum.

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