PHY 201/211 General Physics

1. Circle the right answers. There is only one correct answer for each question.

I. Which of the following is not a proper explanation to the observation:

Observation

Explanation

A

A spaceship in outerspace (far from any other astronomical objects) has to travel with constant velocity, if no rocket is fired.

Newton=s first law of motion.

B

Projectile motion is independent of mass.

All objects have the same acceleration due to gravity, g=9.8 m/s².

C

As a car is turning around a corner, the net force acting on the car cannot be zero.

Both Newton=s first law and second law imply that the net force acting on an object cannot be zero if it is not moving with a constant velocity.

D

The unit Newton (N) is equivalent to kgm/s².

F = ma.

E

For a person standing on the ground, the normal force from the floor equals to the weight of the person in magnitude.

Action and reaction are equal in magnitude.

II.

A pendulum formed by a string of length L and a bob of mass m is raised to a certain angle and then released from rest. At the lowest point, the bob is traveling with a speed of v. What is the tension in the string?

A. mg

B. 0
C.
D.

E. Not enough information to determine.

III. Two marbles, one twice as heavy as the other, are dropped to the ground from the roof of a building. Just before hitting the ground, the heavier marble has

A. as much kinetic energy as the lighter one.

B. twice as much kinetic energy as the lighter one.

C. half as much kinetic energy as the lighter one.

D. four time as much kinetic energy as the lighter one.

E. impossible to determine.

IV. A cart moving at speed v collides with an identical stationary cart on an airtrack, and two stick together after collision. What is their speed after colliding?

A. 0

B. v

C. 0.5v

D. 0.707v

E. None of the above.

V. A disk is rotating at a constant rate about a vertical axis through its center. Point Q is twice as far from the center of the disk as point P is. The angular velocity of Q at a given time is

A. four times as big as P's

B. twice as big as P's

C. the same as P's

D. half as big as P's

E. None of the above.

VI. An ice-skater spins about a vertical axis through her body with her arms held out. The angular speed is and the moment of inertia is I. By drawing her arms in, she can reduce the moment of inertia to 0.8I, what will be her angular speed?

A. 1.6

B. 1.25

D. 0.8

E. None of above.

VII. A hollow and a solid cylinder are released from rest simultaneously at the top of an incline, they roll down the incline without slipping. The two cylinders are made of different materials, but they have the same mass and radius. Which of the following statement is not correct:

A. The hollow cylinder has a larger moment of inertia.

B. The solid cylinder will reach the bottom of the incline first.

C. The net torque acting on each cylinder is the same.

D. The two cylinders have the same angular acceleration.

E. The sum of translational kinetic energy, rotational kinetic energy and potential energy is conserved for both cylinders.

VIII.

Which point has the highest pressure?

A. Point A

B. Point B

C. Point C

D. Point D

E. Point E

	Observation	Explanation
A	A spaceship in outerspace (far from any other astronomical objects) has to travel with constant velocity, if no rocket is fired.	Newton=s first law of motion.
B	Projectile motion is independent of mass.	All objects have the same acceleration due to gravity, g=9.8 m/s².
C	As a car is turning around a corner, the net force acting on the car cannot be zero.	Both Newton=s first law and second law imply that the net force acting on an object cannot be zero if it is not moving with a constant velocity.
D	The unit Newton (N) is equivalent to kgm/s².	F = ma.
E	For a person standing on the ground, the normal force from the floor equals to the weight of the person in magnitude.	Action and reaction are equal in magnitude.