Question

In: Physics

A coin is moving in a horizontal circle in a cone. The cone has height 70...

A coin is moving in a horizontal circle in a cone. The cone has height 70 cm and radius 20 cm. The coin is at a height halfway up. The coefficient of static friction is 0.3. The mass of the coin is 5 g. How fast is the coin moving to stay at this height?If the velocity is halved what will the height of the coin be now?

Solutions

Expert Solution

In triangle ABC

tan = BC/AB

tan = r/h

tan = 20/70

tan = 0.286

= tan-1(0.286)

= 16 deg

m = mass of coin = 5 g = 0.005 kg

us = Coefficient of friction = 0.3

fs = static frictional force = us Fn

Along the vertical direction, force equation is given as

Fn Sin + fs Cos = mg

Fn Sin + (us Fn ) Cos = mg

Fn = mg /(Sin + us Cos)

Fn = (0.005 x 9.8) /(Sin16 + (0.3) Cos16)

Fn = 0.087 N

Along the horizontal direction , force equation is given as

Fn Cos - fs Sin = m v2/r

Fn Cos - us Fn Sin = m v2/r

0.087 Cos16 - (0.3 x 0.087)Sin16 = (0.005) v2/0.20

v = 1.75 m/s


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