PHY 201/211 General Physics

PHY 201/211 General Physics Odd Sections. 9:30-10:20 lecture Final Examination

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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
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7
Total

1. (50 points)

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

I. A person standing in an elevator, in which of the following situations will the normal force from the floor equal to the person's weight?

A. The elevator is ascending at a constant velocity.

B. The elevator is accelerating upward.

C. The elevator is accelerating downward.

D. The elevator is at rest but the person is holding a 30 kg box.

E. The normal force equals to the person's weight in all of above cases.

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

A. A

B. B

C. C

D. D

E. E

III. A racing car running on a circular track requires a frictional force F to maintain the circular motion. If its speed is halved, the required frictional force will be

A. 0.5F

B. 0.25F

C. 2F

D. 4F

E. None of above.

IV. A ball is thrown vertically upward with an initial v₀ and reaches a maximum height of h. To double the maximum height, the initial velocity should be

A. 2v₀

B. 0.5v₀

C. v₀

D. 0.707v₀

E. 1.414v₀

V. Consider the swinging motion of a pendulum. At which point in the figure the acceleration is maximum?

A. A

B. B

C. C

D. D

E. Acceleration is constant.

VI. A mass is attached to the end of a vertical spring and set into simple harmonic motion. If the mass is increased by four times, the period will be

A. increased by four times.

B. decreased by four times.

C. halved.

D. doubled

E. remain the same.

VII. Two masses A and B are hung at the two ends of a rod as shown in the figure. If length of the rod is L and the mass of A is 2kg, what should be the mass of B if the rod is in static equilibrium when pivoted at a point 0.3L from the end of mass A?

A. 0.60 kg

B. 4.67 kg

C. 0.86 kg

D. 0.15 kg

E. Not enough information.

VIII. Which of the following statement is not correct?

A. Electromagnetic wave does not need a medium to propagate.

B. In vacuum, electromagnetic wave propagates as a transverse wave.

C. Sound wave needs a medium to propagate.

D. Sound wave is a transverse wave.

E. Infrared has a longer wavelength than ultraviolet.

IX. Red light has a wavelength of m, what is the corresponding frequency? Speed of sound is 330 ms^-1 and speed of light is 3 X 10⁸ ms^-1.

D. 192 Hz

E. None of above

X. A string with both ends fixed is vibrating at its fundamental (i.e. first harmonic). What is the wavelength if the length of the string is 1m?

A. 2.00m

B. 1.50m

C. 0.67m

D. 0.50m

E. It depends on the frequency of vibration.

2. (25 points)

The block shown in the figures lies on a smooth plane tilted at an angle = 35.0^o to the horizontal. (a) Determine the acceleration of the block as it slides down the plane. (b) If the block slides from rest 12.0m up the plane from its base, what will be the block's speed when it reaches the bottom of the incline? Ignore friction.

3. (25 points)

A uniform disk, such as a record turntable, turns at 5 rev/s around a frictionless spindle. A nonrotating rod, of the same mass as the disk and length equal to the disk's diameter, is dropped onto the freely spinning disk. They then both turn around the spindle with their centers superposed (see figure). What is the angular velocity in rev/s of the combination? (Moment of inertia of a disc is and moment of inertia of a rod rotating abut an axis through its midpoint is . M, R, and L are mass, radius of the disc, and length of the rod respectively.)

4. The mass of a star is given as 810³⁰ kg. There is a planet revolving around the star at a circular orbit of radius 40010⁹m. (Gravitational constant G is given as

a. (10 points)

What is the acceleration of the planet? Give both magnitude and direction.

b. (15 points)

Calculate the speed of the planet, and also the period of revolution.

5. A ball starts from rest and slides down the frictionless ramp at a height of 0.6m (see figure).

a. (13 points)

What will be the speed of the ball when it enters the horizontal section of the frictionless table top?

b. (12 points)

At what distance from the bottom of the table will the 2 kg hit the floor if the table is 1.5 m high?

6. A 10 kg solid sphere of 0.1 m in radius is originally moving on a horizontal surface at a translation velocity of 4 m/s. It later climbs up an incline as shown in the figure. It is rolling without slipping for the whole trip. The moment of inertial of a solid sphere can be calculated as

, where M is the mass and R is the radius of the sphere.

a. (15 points)

Calculate the translational and rotational kinetic energy, and then the total kinetic energy when the sphere is moving on the horizontal surface.

b. (10 points)

How high (h in the figure) will the center of mass of the ball move up the ramp ?

7. A 1 kg mass is attached to the end of a horizontal spring with a spring constant of 250 Nm^-1 . There is no friction between the mass and the horizontal surface in contact. The mass is displaced 4cm away from the natural length of the spring as shown in the diagram. The mass performs simple harmonic motion after it is released from rest.