PHY 201/211 General Physics

PHY 201/211 General Physics Even Sections. 11:00-11:50 lecture Test III

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Answer all problems.

Do not start working until you are told to do so.

Following information may be useful:

formula sheets are also provided at the back of this test.

(Do not write below)

Problem No.	Score
1
2
3
4
Total

1. (25points)

Circle the right answers. Only one choice is correct. No penalty for wrong guess.

I. A cart on a frictionless track is released from rest at point P. At which of the following points the block is moving the slowest? Assume the cart stays on the track all the time.

A. A

B. B

C. C

D. D

E. E

II. Two objects make an elastic collision, which statement is not correct?

A. Momentum is conserved by the collision.

B. The two objects stick together after the collision.

C. Mechanical energy is conserved by the collision.

D. Center of mass of the two objects moves with a constant velocity during the collision.

E. The two objects exert equal and opposite forces on each other during the collision.

III. Which of the following cannot be a unit of power?

A. Watt

B. Joule

C. Nms^-1

D. Kgm²s^-3

E. Js^-1

IV. The gravitational attraction between two objects is F. What will be the attraction if the separation is doubled?

A. 2F

B. 0.5F

C. 4F

D. 0.25F

E None of above

V. Suppose this block is 300m long, and quite steep. If I ride my bicycle up the hill along the zigzag path, which is 600m long, the energy I must expend is

A. one quarter

B. one half

C. equal to

D. double

E four times

the energy I would spend going straight up. Assume no energy loss due to friction or air resistance.

2. (25 points)

A tennis ball of mass m=0.050kg and speed v= 30m/s strikes a wall at 30^o and rebounds with the

same speed at 30^o (see figure). What is the impulse given by the wall? (Note that you have to specify both magnitude and direction.)

3. A roller coaster is released from rest at height h (see figure). It runs through a vertical loop of 40m in radius. Ignore friction and air resistance.

a. (5 points)

What is the normal force acting from the seat on the passenger when the passenger starts to fall out from the cart?

b. (10 points)

What is the minimum speed of the cart at the highest point of the loop to prevent the passenger from falling out?

c. (10 points)

At what height h should the roller coaster be released (from rest) so that it can travel with the minimum speed at the highest point of the loop?

4. Ball A of mass 2kg is released from rest at a height 2m above the horizontal level (see figure).
Ignore friction and air resistance.

a. (10 points)

What is the speed of ball A just before its collision with ball B?

b. (15 points)

If ball B has a mass of 3kg and it is originally at rest. It moves with a velocity of 4.5m/s towards left after the collision. What is the velocity of ball A after the collision?