PHYS1224 Fall 2006

Exam #1 Part A

Name: _______________________________________________________

I . Matching: ________________________________ (78 pts)

II. Fill in the Blank: __________________________ (26 pts)

III. Write the Definitions: ______________________ (18 pts)

IV. Short Answer: __________________________ (12 pts)

V. Derivation: _______________________________ (10 pts)

Total Part I: ___________________________________ (144 pts)

Total Part II: __________________________________ (240 pts)

Total Points: ___________________________________ (384 pts)

Grade: ____________________________________

I. Multiple Choice (3 pts each)

1. An object is moving to the right at constant speed. Which of the following statements must be incorrect?

a) There is just one force acting on the object and it is to the right.

b) There are no forces acting on the object.

c) There are a larger number of forces acting on the object to the right than to the left.

d) There is no net external force acting on the object.

2. While driving from Ft. Worth to Stephenville, Dr. Marble’s car goes through a turn while slowing down. Which of the following best describes the situation:

a) The car has tangential acceleration only.

b) The car has no acceleration.

c) The car has centripetal acceleration.

d) The car has both centripetal and tangential acceleration.

3. A block slides on a frictionless surface along a loop-the-loop shown in the figure.

Circle the correct free-body diagram for the block when it is located at point C (all three share the same coordinate axis)?

4. Using a velocity-time graph, the acceleration of a body can be found by

a) finding the area under the curve

b) finding the slope at a given time

c) finding the difference in the end points of the curve

d) none of these

x

y

5. A person is holding a book in their hands. The reaction force (force described byNewton III) to the weight of the book is:

a) The gravitational pull of the book upon the earth.

b) the force of the person’s hand on the book.

c) the force of the air on the book.

d) the weight of the person.

e) None of these.

6. Which of the following statements are true for a body undergoing uniform circular motion:

a) The tangential acceleration depends on the velocity of the object

b) Uniform acceleration means that there is no net external force on the body.

c) The velocity of the object is constant.

d) None of these are correct.

7. In the figure below, the reaction force to the weight of the block is

a) the force exerted on the block by the inclined plane.

b) the force exerted on the block by friction.

c) the force whose magnitude is (mg) cos .

d) the upward attractive force exerted on the earth by the block.

8. Identical guns fire identical bullets horizontally at the same speed from the same height above level planes, one on the Earth and one on the Moon. Which of the following three statements is/are true?

I. The horizontal distance traveled by the bullet is greater for the Moon.II. The flight time is less for the bullet on the Earth.III. The velocities of the bullets at impact are the same.

a) II only

b) I and II only

c) I and III only

d) II and III only

e) I, II, III

m

9. A boy throws a ball North with a speed of 40 m/s. If the boy is traveling on a train going 30 m/s to the East, what is the speed of the ball as measured by a girl sitting next to the railroad track?

a) 70 m/s b) 10 m/s c) 50 m/s d) none of these

10. A body moves with constant speed in a straight line. Which of the following statements must be true?

a) No force acts on the body.

b) A single constant force acts on the body in the direction of motion.

c) A zero net force acts on the body.

d) Insufficient information to determine the number and types of forces since you don’t know the acceleration of the body.

11. For an acceleration-time graph, the change in the velocity of an object is obtained by

a) finding the area under the curve.

b) finding the slope at a given time.

c) finding the difference in the end points of the curve.

d) none of these.

12. A box is sitting stationary on an incline plane. Which of the following statements about the friction force MUST be true?

a) Its magnitude must equal the box’s weight.

b) Its magnitude must equal the coefficient of static friction times the weight of the box.

c) Its magnitude must equal the coefficient of static friction times the normal force applied to the box.

d) None of these.

13. A man riding in an elevator has an apparent weight which is less than his actual weight. Which of the following statements could be true?

a) The elevator moves upward at a constant speed.

b)The elevator moves downward with increasing speed.

c) The elevator moves downward with decreasing speed.

d) The only explanation is bad precision where the man must have incorrectly read his weight.

14. A net force is exerted on an object towards the South. The statement which might describe this situation is:

a) The object may be moving toward the North, but it will start slowing down.

b) The object will be accelerating to the North

c) The object must be moving to the South.

d) The object is presently moving to the South and has only centripetal acceleration.

15. If two blocks of wood of different weights start together at the same height and slide freely down a frictionless inclined plane, which of the following will be true?

a) The less massive object will reach the bottom first as it has less resistance to gravity.

b) They will have equal accelerations.

c) They will have unequal accelerations, but the forces acting on the blocks are the same.

d) The object with the greatest weight will reach the bottom first due to the greater force of gravity.

16. Two balls are the same size, but one has twice the inertia as the other. The ballsare dropped from the top of a space craft at the same instant of time on an uncharted planet. The relative time it takes for the balls to reach the ground will be

a) largest for the ball with the least inertia.

b) smallest for the ball with less inertia.

c) smallest for the ball with the least weight.

d) None of these.

17. Two bikes are traveling in opposite directions at the same speed of 20 km/hr as shown below. When two bikes are 80 km apart, a bee begins flying from one wheel to the other at 50 km/hr. When it gets to the wheel of one bike, it abruptly turns around and flies back to touch the first wheel, and then turns around and keeps repeating the back-and-forth trip until the bikes meet, and squish! How many kilometers did the bee travel in its total back-and-forth trips?

a) 20 km b) 40 km c) 80 km d) 100 km e) 50 km

18. A 5000 kg truck traveling at high speed collides with a 10,000 kg tractor trailertraveling at low speed. Which of the following statements is true?

a) You have to know the speeds of the vehicles to determine which applies the greatest force.

b) The tractor trailer applies the greatest force as it is more massive. c) The truck applies the greatest force since it is the faster vehicle

d) None of the above.

19. Dr. Daffy duck plots his experimental data and finds that his results are linear on a semi-log plot. Thus, the dependent variable shows

a) an exponential dependence

b) a power dependence

c) a linear dependence

d) none of these

20. A crate is moving to the right on a conveyor belt without slipping. The conveyor belt maintains a constant speed. The force of friction on the crate is

a) to the right

b) zero

c) to the left

d) can not be answered without more information

21. You are pushing a wooden crate across the floor at constant speed. You decide to turn the crate on end, reducing by half the surface area in contact with the floor. In the new orientation, to push the same crate across the same floor with the same speed, the force that you apply must be about

a) four times as great

b) twice as great

c) equally great

d) half as great

e) one-fourth as great

22. A basketball player makes contact with the floor after grabbing a rebound, he continues downward at slower and slower speeds until he comes to a stop. During the time that he is headed downward, the force of the floor on his shoes is

a) bigger than his weight.

b) equal in magnitude and opposite in direction to his weight.

c) less than his weight.

d) zero.

23. Consider a puck sliding on a smooth wooden plank and slowing down to a stop because of the friction between the puck and the wooden plank. If we plot the puck's position versus time, we find the graph is

a) a parabola

b) a decaying exponential function

c) a straight line

d) none of the above

24. You may have heard the statement "Friction opposes motion". Concerning all types of friction forces, this statement is

a) never true.

b) always true.

c) true in some cases, false in others.

25. In the 17th Century, Otto von Guricke, a physicist in Magdeburg, fitted two hollow bronze hemispheres together and removed the air from the resulting sphere with a pump. Two eight-horse teams could not pull the halves apart even though the hemispheres fell apart when air was re-admitted. Suppose von Guricke had tied one team of horses to one side and bolted the other side to a heavy tree trunk. In the case, the tension on the hemispheres would be

a) twice what it was before.

b) exactly the same as before.

c) half what it was before.

d) can't be determined with the information provided.

26. You throw a ball straight up. After you have released it, just before it reaches its maximum height, what force(s) are acting on the ball?

a) Gravity (down)

b) Gravity (down) and inertia (up)

c) Gravity (down) and the force of the throw (up)

d) Inertia (up)II. Fill in the Blank (2pts each)

1. What are the SI units for the following physical quantities:

A. Time-rate-of-change of the mass on an object

_______________________________________________________

B. Acceleration ______________________________________________________

C. Inertia ____________________________________________________________

D. Displacement vector ________________________________________________

E. Time _____________________________________________________________

F. The constant G in Newton’s Universal Law of Gravitation shown below where M1 and M2 are the masses of two point objects 1 and 2, F is gravitational force and r is the distance between the objects.

___________________________________________________________

2. Write the condition required for the kinematics equations to be valid.

3. Write the vector equation that defines the instantaneous acceleration of a particle:

4. Write the vector equation that defines the average velocity of a particle:

5. What does the word centripetal mean:

6. I developed the law of sliding friction.

7. I was the first scientist to make extensive use of the microscope and performed experiments with inclined planes and water clocks.

______________________________________________________________

8. I am the great French physicist who developed the concept of linear momentum that laid the ground work for Newton's 3rd Law:

__________________________________________________________________

III. Write the definition ( 6 pts each )

1. State Newton's First Law:

2. State Newton's 2nd Law (Mathematically) for a particle:

3. State Newton's Third Law:

IV. Short Answer (4 points each)A. More than 300 years ago, Isaac Newton claimed that the moon is accelerating

toward the planet Earth. Explain how we know that the moon is accelerating toward the earth and why it hasn’t hit the earth over the past 300 years.

B. An apple is dropped from some height above the Earth’s surface. Neglecting air resistance, how much does the apple’s speed increase each second during its descent?

C. In an attempt to define Newton’s third law, a student states that the action and reaction forces are equal in magnitude and opposite in direction to each other. If this is the case, how can there ever be a net force on an object?

V. Derivation (10 points):A particle of mass m at t = 0 is located at x = b and traveling at a speed of c in the +x direction. Assuming the force acting upon the particle in the x-direction at time t is , derive the equation giving the position of the particle as a function of time.