Physics 201 MWF10:20 Fall 2002 (Ford)

Exam III Chapts 8--11 Cutnell and Johnson 5th ed


Show all your work. Partial credit will be given if earned. Write your answers in the blanks provided.

(18 pts) 1. A block of mass m = 0.50 kg is attached to a horizontal spring that has spring constant k = 1200 N/m. The block moves on a horizontal frictionless surface. The block is moving back and forth in simple harmonic motion. When the block is at x = 0.16 m, its kinetic energy is 6.0 J.

a) What is the amplitude of the block's motion?

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b) What is the maximum speed of the block during its motion?

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(20 pts) 2. When a rock of density 2200 kg/m³ is suspended in air at the end of a string, the tension in the string is 18 N. When the rock is totally immersed in a liquid, the tension in the string is 12 N.

a) What is the volume of the rock?

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b) What is the buoyancy force that the liquid exerts on the rock when the rock is totally immersed in it?

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c) What is the density of the liquid?

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(20 pts) 3. A uniform disk (I =mr²/2) has radius r = 0.30 m and mass 12 kg. The disk is initially rotating at a constant angular speed of 8.0 rev/s about an axis through its center. At t = 0 a person pushes an axe blade against the rim of the disk and this produces a constant friction force of 4.0 N that is tangent to the rim of the disk. This friction force slows the rotation of the disk and is continued to be applied until the wheel stops rotating.



a) Before the friction force is applied, what is the tangential speed of a point on the disk 0.20 m from the axis?

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b) Through how many revolutions does the disk turn in the first 5.0 s after the friction force is applied?

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c) What is the magnitude of the centripetal acceleration of a point on the rim of the disk at t = 5.0 s?

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d) What is the magnitude of the tangential acceleration of a point on the rim of the disk at t = 5.0 s?

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(18 pts) 4. A bowling ball is rolling along level ground with a constant translational speed v = 12 m/s. The bowling ball rolls without slipping and is a uniform solid sphere, with moment of inertia I = 2mr²/5 for an axis through its center. The bowling ball comes to a hill and rolls up it. What vertical height will the ball travel up the hill before it momentarily comes to rest?



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(24 pts) 5. An aluminum bar 8.0 m long is attached to the wall by a frictionless hinge. A 300 N object is suspended from the middle of the bar. The weight of the bar can be neglected. The bar is held in place at an angle of 65° above the horizontal by a cable that runs between the end of the bar and the wall. The cable makes a 37° angle with respect to the bar and therefore is at 28° below the horizontal.



a) For an axis at the hinge, what is the magnitude of the torque on the bar produced by the weight of the suspended object?

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b) What is the tension in the cable?

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c) What is the vertical component of the force the hinge exerts on the bar?

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