A person’s center of mass is easily found by having the person lie on a reaction board. A horizontal, 2.5-m-long, 6.1 kg reaction board is supported only at the ends, with one end resting on a scale and the other on a pivot. A 60 kg woman lies on the reaction board with her feet over the pivot. The scale reads 25 kg. What is the distance from the woman’s feet to her center of mass?
Woman’s feet to centre of mass is at 91.5 cm .
The mas of reaction board 6.1 kg
Length = 2.5 m
Mass of woman = 60 kg
Her feet on pivot, the reading of scale is 25 kg
Lets understand with a diagram and solve the problem
For a system to be in equilibrium , clock-wise and anticlockwise torque should be same.
We have to use weight by multiplying mass with g
Cancel g and solve for x, we get
x=0.915 m = 91.5 cm.
A merry-go-round is a common piece of playground equipment. A 3.0-m-diameter merry-go-round with a mass of 250 kg is spinning at 20 rpm. John runs tangent to the merry-go-round
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Starting from rest, a 12-cm-diameter compact disk takes 3.0 s to reach its operating angular velocity of 2000 rpm . Assume that the angular acceleration is constant. The disk's moment of inertia is .
a. How much net torque is applied to the disk?
b. How many revolutions does it make before reaching full speed?
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