When the play button is pressed, a CD accelerates uniformly from rest to 410rev/

Question

When the play button is pressed, a CD accelerates uniformly from rest to 410rev/min in 5.0 revolutions. If the CD has a radius of 6.0cm and a mass of 20g , what is the torque exerted on it? Express your answer using two significant figures. An 85-kg person stands on a lightweight ladder, as shown in the figure(Rgurel). The floor is rough; hence, it exerts both a normal force f1, and a frictional force f2, on the ladder. The wall, on the other hand, is frictionless; it exerts only a normal force Suppose the person climbs higher on the ladder. As a result, is the ladder more likely, less likely, or equally likely to slip? Choose the best explanation from among the following: The magnitude of must increase as the person moves upward. The forces are the same regardless of the person's position. more likely less likely equal likely When the person is higher, the ladder presses down harder on the floor. Consider the pulley-block system shown in the fiaure(Figure 1). Is the tension in the string on the left-hand rotating system greater than, less than, or equal to the weight of the mass attached to that string? Choose the best explanation from among the following: The string rotates the pulley in addition to supporting the mass. The mass accelerates downward. The mass is in free fall once it is released.

Explanation / Answer

Number 1)

First we need to convert 410 rev/min (2pi rad/rev and 60 sec per min) = 42.935 rad/s

5 revs times 2pi = 31.42 radians

Torque = I(alpha)

Find alpha...

wf2 = wo2 + 2(alpha)theta

(42.935)2 = 0 + 2(aplha)(31.42)

alpha = 29.34 rad/s2

Torque = (.5)(.02)(.06)2(29.34)

.0011 Nm (1.1 X 10-2 Nm)

Number 2)

Since climbing higher also moves you further away horizontally from the base, you increase torque and are therefore more likely to slip

The forces are the same regardless of position...Its the distance that is increasing and torque = Force times distance so torque increases.

Number 3)

The tension is less than the weight

The mass accelerates downward

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