Physics 201 MWF10:20 Fall 1995 (Ford)
Exam II Chapts. 6-8 in SZY College Physics

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

(20 pts) 1. A block with mass 2 kg is placed against a horizontal compressed spring. The spring is released and the block travels to the right along a horizontal surface. When the block has traveled 0.80 m from its initial position against the compressed spring, its speed is 2.5 m/s and it is no longer in contact with the spring. If the amount of potential energy initially stored in the spring was 8.0 J, what is µ_k, the coefficient of kinetic friction between the block and the horizontal surface?

Ans. ___0.112___


(22 pts) 2. One end of a very light string that is 0.40 m long is attached to the ceiling. The other end is attached to a small ball of mass m. The ball is put into motion in a horizontal circle with a constant speed. While the ball is revolving in the horizontal circle the string makes an angle of 37° with the vertical and the tension in the string is 3.0 N.

a) What is the mass m of the ball?

Ans.___0.245 kg___

b) What is the magnitude of the acceleration of the ball?

Ans. ___7.35 m/s²___

c) What is the speed of the ball?

Ans. ___1.33 m/s___

d) How much time does it take for the ball to complete one revolution?

Ans. ___1.13 s___


(20 pts) 3. A block of mass 2 kg sits on a horizontal tabletop. This block is connected by a light rope that passes over a frictionless, massless pulley to a hanging block of mass 4 kg. There is friction between the 2 kg block and the table top. The system is released from rest. During the displacement of the 2 kg block from its initial position to a point 0.50 m to the right the friction force on the 2 kg block does -6.0 J of work. At the instant when the 2 kg block has moved 0.50 m to the right and the 4 kg block has descended 0.50 m, what is the speed of the 4 kg block?

Ans.___2.13 m/s___


(16 pts) 4. On a horizontal frictionless surface block A that is traveling east collides with block B that is traveling north. Block A has mass m_A = 4.0 kg and block B has mass m_B = 6.0 kg. As a result of the collision the two blocks stick together. Immediately after the collision the combined object is moving with speed v₂ in a direction 37° N of E. The speed of block A before the collision was 8.0 m/s.

a) What is the speed v₂ of the combined object after the collision?

Ans. ___4.0 m/s___

b) What was the speed v_B1 of block B before the collision?

Ans. ___4.0 m/s___


(22 pts) 5. A block of wood with mass 1.96 kg hangs at rest at the end of a long, massless rope. A bullet with mass 0.04 kg and speed v₀ is fired into the block and remains embedded in it. As a result of the collision the block swings on the end of the rope from point A to point B. At point B the speed of the block is instantaneously zero and the center of the block is 0.18 m higher than at point A. When the block is at point B the rope makes an angle of 20° with the vertical.

a) What is the speed of the block immediately after the collision, before it has had time to move?

Ans. ___1.88 m/s___

b) What is the speed of the bullet just before the collision?

Ans. ___93.9 m/s___

c) At the instant when the block (with the bullet embedded inside it) is at point B, what is the tension in the rope?

Ans. ___18.4 N___