# First Hour Exam

## September 19, 1997

Enter all your answers in the "scantron sheet" or the "bubble sheet". Turn in only that sheet. Anything you write on this exam will not be seen or used or considered or graded. Be sure your name is on the "bubble sheet" you hand in. Be sure your name is bubbled-in. Be sure your answers are recorded correctly.

For every question, also consider the following as a possible answer:

e) none of the above

Possibly useful information:

v = x / t

a = v / t

v = vi + a t

x = xi + vi i t + (1/2) a t2

v = r w

F = ma

F12 = &endash; F21

w = mg

g = 9.8 m/s2 Å 10 m/s2

1. Kinematics is a description of motion. Motion was first well understood

a) by Aristotle and the ancient Greeks

b) by Ptolemy in Egypt

c) by Galileo in Italy

d) not until the beginning of the twentieth century

2. To measure the time needed to investigate motion,

a) Aristotle used the pendulum clock which had just been invented

b) Ptolemy used a sundial

c) Galileo invented his own water clocks

d) Newton invented the pendulum clock

3. What is the average speed of a motorcycle that travels 20 m in 2 s?

a) 40 m/s

b) 20 m/s

c) 10 m/s; v = 20 m / 2 s = 10 m/s

d) 9.8 m/s

4. What is the average speed of a car that travels 45 km in 3 h?

a) 135 km/h

b) 15 km/h; v = 45 km / 3 h = 15 km/h

c) 10 km/h

d) 9.8 km/h

5. Consider a train that has an acceleration of 3 m/s2. Initially, at time t = 0, it has a velocity of vi = 10 m/s. What is its speed at t = 3 s?

a) 40 m/s

b) 30 m/s

c) 23 m/s

d) 19 m/s; v = vi + a t = 10 m/s + (3 m/s2) (3 s) = (10 + 9) m/s = 19 m/s

6. Consider a car that starts at rest and accelerates at 2 m/s2 for 3 seconds. At that time, t = 3 s, how fast is it going?

a) 12 m/s

b) 9 m/s

c) 6 m/s; v = vi + a t = 0 + (2 m/s2) (3 s) = 6 m/s

d) 3 m/s

7. Consider a car that starts at rest and accelerates at 2 m/s2 for 3 seconds. At that time, t = 3 s, how far has it gone?

a) 12 m

b) 9 m; x = xi + vi t + (1/2) a t2 = 0 + 0 + (1/2) (2 m/s2) (3 s)2 = 9 m

c) 6 m

d) 3 m

8. Consider a ball that is thrown upward at the edge of a canyon with an initial velocity of 20 m/s. Three seconds later, what is its velocity?

a) 30 m/s

b) 15 m/s

c) - 10 m/s; v = vi + a t = 20 m/s + ( - 10 m/s2) (3 s) = (20 - 30) m/s = - 10 m/s

d) - 30 m/s

9. Consider a ball that is thrown straight upward at the edge of a canyon with an initial velocity of 20 m/s. Three seconds later, where is it located? Take its initial position, at the edge of the canyon, to be the origin; that is, yi = 0.

a) 30 m

b) 15 m; y = yi + vi t + (1/2) a t2 = 0 + (20 m/s) (3 s) + (1/2) (- 10 m/s2) (3 s)2 = (0 + 60 - 45) m = 15 m

c) &endash; 10 m

d) &endash; 30 m

10. Consider a ball that is thrown horizontally from the edge of a building with an initial velocity of 20 m/s. The building is 5 m above the driveway below. How far from the building does the ball strike the driveway?

a) 5 m

b) 10 m

c) 15 m

d) 20 m

y = (1/2) a t 2

- 5 m = (1/2) ( - 10 m/s 2) t 2 = (- 5 m/s2) t 2

1 s2 = t2

t = 1 s

x = vx t = (20 m/s) (1 s) = 20 m

11. When a ball or stone or other object is thrown or hit or fired, and air resistance can be neglected, the resulting motion is known as projectile motion The path of an object in projectile motion is

a) a straight line

b) a hyperbola

c) a parabola

d) a quadrant of a circle

12. Projectile motion is a combination of

a) horizontal motion with constant, non-zero acceleration and vertical motion with constant velocity

b) horizontal motion with constant non-zero acceleration and vertical motion with constant, non-zero acceleration

c) horizontal motion with constant velocity and vertical motion with constant, non-zero acceleration

d) horizontal motion with constant velocity and vertical motion with constant velocity

13. Consider a ball thrown from a level surface with an initial upward velocity of 10 m/s and an initial horizontal velocity of 5 m/s. How long is the ball in the air?

a) 1.0 s

b) 1.5 s

c) 2.0 s

d) 4.0 s

Time to top: v = 0

v = vi + a t = 10 m/s + ( - 10 m/s2) (ttop) = 0

0 = 10 - 10 t top

t top = 1 sec

Total time in the air

ttotal = 2 ttop = 2 s

14. Consider a ball thrown from a level surface with an initial upward velocity of 10 m/s and an initial horizontal velocity of 5 m/s. Where does it land? That is, measured from its initial position, where does it come back to and strike the level surface?

a) 5 m

b) 10 m

c) 15 m

d) 20 m

From question 13, we already know the ball is in the air for t = 2 sec

x = vx t = (5 m/s) ( 2 s) = 10 m

15. Newton's First Law of Motion states that, in the absence of a net force, an object in motion will

a) eventually come to rest

b) continue in motion but slow down until it stops

c) continue in motion with the same speed along the same straight line

d) continue along the same straight line with a decrease in speed

16. Mass is a measure of

a) the volume of an object

b) the size of an object

c) how difficult it is to change the motion of an object

d) the velocity of an object

17. The weight of an object is

a) the same thing as the mass of an object

b) the sum of all the forces on an object

c) the force of gravity on an object

d) always less than the mass, even in a vacuum

18. The net force on a 1-kg object, at rest, is

a) 9.8 N

b) 4.9 N

c) 1.00 N

d) zero

19. The net force on a 1-kg object, in free fallt, is

a) 9.8 N

b) 4.9 N

c) 1.00 N

d) zero

20. Harry the Painter has a weight of 500 N. When he is suspended as shown in the sketch here, what is the tension in the rope?

a) 1000 N

b) 500 N

c) 250 N

d) 25 N

21. A force of 24 N acts on an object whose mass is 6 kg. This causes the object to accelerate at

a) 2 m/s2

b) 4 m/s2

c) 6 m/s2

d) 10 m/s2

22. A car, with mass of 1,000 kg, accelerates at 2 m/s2. The net force exerted on the car must be

a) 500 N

b) 1,000 N

c) 2,000 N

d) 10,000 N

23. The weight of a 1,000-kg car is

a) 500 N

b) 1,000 N

c) 2,000 N

d) 10,000 N

24. A fireman, whose weight is 500 N, slides down a pole with an acceleration of 3 m/s2. The forces that act on him are his weight pulling him down and the force of friction pulling up on him to slow him down. The force of friction must be

a) 90 N

b) 150 N

c) 350 N

d) 500 N

25. Suppose you are driving along in an open car and throw a ball straight up into the air. While the ball is still in the air you step on the accelerator. Where does the ball land relative to the car?

a) behind the car

b) back into the car

c) in front of the car