Your Name: _______________________ PHY203

Exam #3

Student ID: ________________________ Chapters 8-10,12

Tues., 4/17/01

Lecture Time: 1p.m. 2p.m.

1. A 2kg block is traveling along in the positive x-direction at an initial speed of 5m/s. A 1kg block traveling in the negative y-direction with an initial speed of 4 m/s collides with the 2 kg block and sticks.

a. Using the coordinate system shown above, find both the x and components

(magnitude and sign) of the total momentum just before the collision.

b. What are the x and y components of the momentum of the 2-block system

after the collision?

c. Find the x and y components (magnitude and direction) of the velocity of the

2-block system just after the collision has taken place.

d. Find the change in kinetic energy of the system before and after the collision.

2. A disk of mass 10 kg and radius 0.5 m is at rest. A force of 10 N is applied at the edge of the disk at an angle of 60^o as shown.

a. Find the magnitude of the torque, t. Will the torque cause the disk to rotate in a clockwise or counterclockwise direction?

b. Calculate the moment of inertia, I, of the disk.

c. Calculate the angular acceleration, a, of the disk.

d. Calculate the total angular rotation, q, in radians that the disk makes after the

torque has been applied for 10 seconds.

e. Calculate how many revolutions the disk makes in the same 10 seconds.

3. A ball of mass 2kg traveling at a speed of 2m/s strikes a rod of length 2m and mass 3 kg and sticks to it. The rod is hanging from and pivots about an axis at its top end (labeled A).

a. Calculate the moment of inertia of the rod about its end.

b. Calculate the angular momentum of the system about point A just before the collision.

c. What is the angular momentum of the system after the collision?

d. Calculate the moment of inertia of the ball+rod system.

e. Calculate the angular velocity of the ball+rod system after the collision.

f. Calculate the kinetic energy of the system just before and after the collision.

5. A ball with mass 1kg and speed 2m/s traveling in the positive x-direction hits

and sticks to a block with mass 2kg and initial speed 1m/s in the same direction.

a. Calculate the initial momentum of the ball plus block system just before the collision and write it in vector form.

b. What is the momentum of the system just after the collision?

c. Calculate the velocity to the ball+block combo after the collision and write it in vector form.

d. Calculate the kinetic energy of the system before and after the collision.

6. A ball of mass 2kg is suspended from a hinged massless bar 1m in length and two strings, as shown below.

a. On the diagram above, sketch the forces on the bar due to the wall.

b. Calculate the tension in the lower string, T₁.

c. Using the coordinate system given above, write down Newton’s equations for the x- and y-components of the forces on the massless bar.

d. Write down the torque equation for the bar pivoting about the hinge.

e. Use the torque equation from part c., to calculate the tension in the upper string, T₂.

f. Calculate the x- and y-components of the force of the wall on the bar and write this force in vector form.

PHY203

Exam #3

Crib Sheet

Chapters 8-10,12

(Note: Use 9.81 m/s2 for g, the acceleration due to gravity.)

For a vectors A,B,C with magnitude A,B,C and direction:

If C = A x B ; C = ABsinq with direction of C given by the right hand rule

torque: t = r x F

angular momentum: L = r x p p = mv

parallel axis theorem: I = I_CM + Mh²