Phys-1100 Physics I Quiz 1 October 4, 1999

NAME ______INSTRUCTOR ______SEC #___

PHYS-1100 PHYSICS I QUIZ 1 OCTOBER 4, 1999

NAME ______INSTRUCTOR ______SEC #___

There are 7 different pages in this quiz. Check now to see that you have all of them.

CREDIT / GRADE
PART A / 40%
PART B / 20%
PART C / 40%
TOTAL / 100%

All work and answers must be given in the spaces provided on these pages.

PART A. Each question is worth 5%. In the space provided, to the left of the question number, write the letter corresponding to the best answer to the question.

___ 1. A person initially at point P in the illustration stays there a moment and then moves along the axis to Q and stays there a moment. She then strolls to R, stays there a moment, and then runs quicklyback to P. Which of the position vs. time graphs below correctly represents this motion?

___ 2. a, b, and c are three vectors related by the vector equation a + b = c. The magnitudes of the vectors are a, b, and c, respectively. Which of the following are possible relationships between the magnitudes of the three vectors?

I. a + b = cII. a – b = cIII. a² + b² = c²

only ID. either I or III, but not II
only IIE. either I, or II, or III
only III

___ 3. When an object travels in a circular path at constant speed, the direction of its acceleration is:

A. outward, away from the center of the circle.

B. inward, toward the center of the circle.

C. tangent to the circle, in the direction of its velocity.

D. tangent to the circle, in the direction opposite to its velocity.

E. no direction, the acceleration is zero

___ 4. The sketch below shows a block of mass m on an inclined plane that makes an angle  with the horizontal direction. The block is being held stationary by the force of static friction between the block and the plane. The coefficient of static friction between the block and the plane is s. The magnitude of the net force exerted on the block is:

A. smg cos D. mg cos 

B. smg sin E. mg sin 

C. zero

___ 5. When an object is thrown downward with a speed that is greater than its terminal speed, the direction of the acceleration of the object is:

A. upward.

B. downward.

C. no direction, the acceleration is zero..

D. need to know the terminal speed to answer.

E. it is impossible to throw the object at a speed greater than its terminal speed

___ 6. When an object travels in a circular path of radius R at constant speed v, the work done on the object by the centripetal force is:

D. zero, because the displacement is zero after one revolution

E. zero, because the centripetal force is always perpendicular to the displacement

___ 7. The graph below shows the potential energy U for a particle moving on the x axis.

Which of the following five graphs correctly gives the force F exerted on the particle?

___ 8. A block is pushed across a rough horizontal table top at constant speed by an external force. There is a frictional force between the table and the block. Which one of the following statements is not true?

A. The gravitational potential energy of the block is constant.

B. The kinetic energy of the block is constant.

C. The mechanical energy of the block is constant.

D. The internal energy of the block increases.

E. The external force does positive work.

PART B.

1. (10%) The graph of v versus t shown is for a particle in straight line motion. In the table provided, indicate whether the net force exerted on the particle, F, and the total work done on the particle, W, are positive (+), negative (–), or zero (0), in each of the intervals, 0 to 1 s, 1 s to 2 s, 2 s to 3 s, 3 s to 4 s, and 4 s to 5 s.

0 to 1 s / 1 s to 2 s / 2 s to 3 s / 3 s to 4 s / 4 s to 5 s

F

W

2. (10%) A stone is thrown from a cliff that is 15 m high, and follows the path shown in the diagram. The magnitude of the initial velocity of the stone is v0 = 25 m/s. The horizontal component of the initial velocity is v0x = 15 m/s. Assume there is no air resistance in this problem.

a) (2%) Draw an arrow at point P that points in the direction of the stone’s velocity at that point. Label the arrow v. If the velocity is zero, write v = 0 at point P.

b) (2%) What is the magnitude of the stone’s velocity at point P?

vP = ______

units

c) (2%) Draw an arrow at point P that points in the direction of the stone’s acceleration at that point. Label the arrow a. If the acceleration is zero, write a = 0 at point P.

d) 2%) What is the magnitude of the stone’s acceleration at point P?

aP = ______

units

e) (2%) Draw an arrow at point Q that points in the direction of the stone’s velocity at that point. Label the arrow v. If the velocity is zero, write v = 0 at point Q.

PART C. You must show all your work or state your reasoning in order to receive credit.

1. (40%) The sketch shows a massless spring that was compressed to point Q, a distance d from its equilibrium length. The spring was held in that position, and the steel ball shown was placed on top of it. When the spring was released, it shot the ball into the air. Ignore air resistance in this problem.

a) (7%) At the instant the spring was released, at Q,it exerted an upward force of 30 N on the ball, and the mass of the ball is 0.50 kg. Draw a free body force diagram for the ball at the instant that the spring was released.

b) (7%) Find the magnitude of the net force that acted on the ball at the instant that the spring was released.

Fnet = ______

units

c) (6%) Find the magnitude of the acceleration of the ball at the instant that the spring was released.

a = ______

units

d) (7%) When the top of the spring reached point P, the spring was no longer compressed, and the ball’s speed was 4.0 m/s. The ball then continued upward, free of the spring. Find the distance that the ball rose above point P.

y = ______

units

e) (3%) The direction of the ball’s acceleration at point P was: (Circle the correct choice.)

UPWARDDOWNWARDZERO

f) (10%) Find d, the distance the spring was compressed before it was released.

d = ______

units