On (Figure 1) there is a photograph of a girl pushing on a large stone sphere. T

Question

On (Figure 1) there is a photograph of a girl pushing on a large stone sphere. The sphere has a mass of

8200 kg and a radius of 90 cm and floats with nearly zero friction on a thin layer of pressurized water.

Suppose that she pushes on the sphere tangent to its surface with a steady force of F = 55N and that the pressured water provides a frictionless support. How long will it take her to rotate the sphere one time, starting from rest?

Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

Moment of Inertia=2/5*M*R^2

=2/5*8200*0.9^2

=2656.8 kg-m^2

Torque=r*F

=0.9*55

=49.5 N-m

Now, Torque=I*alpha

alpha=0.0186 rad/s^2

Now 2*pi=1/2*alpha*t^2

t=sqrt(4*pi/(0.0186))

=26 s ans

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