Physics 201 MWF10:20 Fall 2004 (Ford)

Exam III Chapts 8--11 Cutnell and Johnson 6th ed


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

(18 pts) 1. A wheel rotates with constant angular acceleration about an axis through its center. The wheel starts from rest and rotates through 0.18 rev in 2.0 s.

a) What is the angular acceleration of the wheel, in rev/s²?

Ans. ____0.090 rev/s²___

b) At t = 2.0 s, what is the linear speed of a point on the wheel that is 0.20 m from the axis?

Ans. ___0.226 m/s___

c) At t = 2.0 s, what is the magnitude of the total resultant linear acceleration of a point on the wheel that is 0.20 m from the axis?

Ans. ____0.279 m/s²________________


(16 pts) 2. One end of a uniform beam is attached to a wall by a frictionless hinge. The beam is held at an angle of 53° above the horizontal by a horizontal rope that is connected between the top end of the beam and the wall. The tension in the rope is 140 N.



a) What is the weight of the beam?

Ans. ____372 N____

b) What is the magnitude of the resultant force that the hinge exerts on the beam?

Ans. ___397 N____


(16 pts) 3. A wheel rotates without friction about a horizontal axis at the center of the wheel. A constant tangential force equal to 80 N is applied to the rim of the wheel. The wheel has radius r = 0.12 m. Starting from rest the wheel has an angular speed of 12 rev/s after 2.0 s. What is the moment of inertia of the wheel?



Ans.____0.255 kg·m²____


(16 pts) 4. A thin rod has length 0.70 m and rotates on a frictionless tabletop about an axis that is perpendicular to the rod at one end. The rod has moment of inertia 0.026 kg·m² for rotation about this axis. Initially a small bug is standing on the rod at the axis and the rod has an angular velocity of 0.40 rad/s. The bug slowly crawls to the other end of the rod and when the bug reaches this point the angular velocity of the rod is 0.30 rad/s.



a) What is the mass of the bug?

Ans. ____0.018 kg_______

b) What is the total kinetic energy of the system (bug + rod) when the bug is at the axis?

Ans. ___2.08 × 19^-3 J____

c) What is the total kinetic energy of the system (bug + rod) when the bug has reached the other end of the rod?

Ans. ______1.56 × 19^-3 J_____


(18 pts) 5. A small block of mass 0.20 kg is attached to a horizontal spring. The block moves on a horizontal frictionless surface and is moving with simple harmonic motion that has a period of 1.8 s. When the block is at x = 0.080 m, its speed is 0.30 m/s.

a) What is the magnitude of the acceleration of the block when it is at x = 0.080 m?

Ans. ____0.975 m/s²____

b) What is the amplitude of the motion of the block?

Ans. ___0.117 m_____

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

Ans. ____0.410 m/s____


(16pts) 6. When a 3.0 kg block is suspended from a string and totally immersed in water (density 1000 kg/m³) the tension in the string is 22.0 N. When the block is totally immersed in ethyl alcohol (density 806 kg/m³), what is the tension in the string?



Ans. ____23.4 N___