1995 Physics Olympiad Screening Test (1-20)

1. The accompanying figure is a graph of an object’s position as a function of time.

PO1995ques1diagram.gif (1860 bytes)

Which lettered segment corresponds to a time when the object has a negative acceleration?

A. A
B. B
C. C
D. D
E. E

2. A car is moving at a constant velocity to the right along a straight level highway. Just as the car passes a cliff, a rock falls straight down in the cliff’s reference system. Which of the accompanying curves best depicts the path the rock takes in the car’s reference system?

PO1995ques2ans.gif (1866 bytes)

3. Three blocks – 1, 2, and 3 – rest on a horizontal frictionless surface, as shown in the accompanying figure. Each block has a mass m, and the blocks are connected by massless strings. Block 3 is pulled to the right by a force F.

The resultant force on block 2 is:

A. Zero
B. ¹/₃ F
C. ¹/₂ F
D. ²/₃ F
E. F

4. Which solid vector in the accompanying figures best represents the acceleration of a pendulum mass at an intermediate point in its swing?

PO1995ques4ans.gif (2455 bytes)

5. A mass attached to a horizontal massless spring is displaced 16 cm to the right of its equilibrium position and released from rest. At its 16 cm extension, the spring-mass system has 1.28 joules of potential energy.

PO1995ques5diagram.gif (1765 bytes)

Upon release, it slides across a rough surface and comes momentarily to rest 8 cm to the left of its equilibrium position. How much mechanical energy was dissipated by friction?

A. 0.16 J
B. 0.32 J
C. 0.64 J
D. 0.96 J
E. 1.12 J

6. Two identical masses m are connected to a massless string which is hung over two frictionless pulleys as shown.

PO1995ques6diagram.gif (1312 bytes)

If everything is at rest, what is the tension in the cord?

A. Less than mg.
B. Exactly mg.
C. More than mg but less than 2mg.
D. Exactly 2mg.
E. More than 2mg.

7. Car A and car B are both traveling down a straight highway at 25 m/s (about 56 mph). Car A is only 6.0 m behind car B. The driver of car B brakes, slowing down with a constant acceleration of 2.0 m/s² . After a time 1.2 s, the driver of car A begins to brake, also at 2.0 m/s² . What is the relative velocity of the two cars when they collide? Hint: Both cars are still moving forward when they collide.

A. 2.4 m/s
B. 5.0 m/s
C. 9.5 m/s
D. 21 m/s
E. 24 m/s

8. During the collision between car A and car B described in Problem # 7 above, which car experiences the greater change in momentum?

A. The more massive car.
B. The less massive car.
C. Car A because its velocity at the start of the collision is greater.
D. Car B because its velocity at the start of the collision is less.
E. Both cars experience the same magnitude of momentum change.

9. A 70 kg hunter ropes a 350 kg polar bear. Both are initially at rest, 30 m apart on a frictionless and level ice surface. When the hunter pulls the polar bear to him, the polar bear will move:

A. 5 m
B. 6 m
C. 15 m
D. 24 m
E. 25 m

10. A bullet of mass m is fired at a block of mass M initially at rest. The bullet, moving at an initial speed v, embeds itself in the block. The speed of the block after the collision is:

11. The driver of a 1000 kg car tries to turn through a circle of radius 100 m on an unbanked curve at a speed of 10 m/s. The maximum frictional force between the tires and the slippery road is 900 N. The car will:

A. Slide into the inside of the curve.
B. Make the turn.
C. Slow down due to the centrifugal force.
D. Make the turn only if it speeds up.
E. Slide off to the outside of the curve.

12. A solid cylinder weighing 200 N has a fixed axis and a string wrapped around it. The string is pulled with a force equal to the weight of the cylinder. The acceleration of the string is approximately:

A. 10 m/s²
B. 20 m/s²
C. 30 m/s²
D. 40 m/s²
E. 50 m/s²

13. A spinning ice skater has an initial kinetic energy (½)Iw². She pulls in her outstretched arms, decreasing her moment of inertia to (¼)I. Her new angular speed is:

A. ¼ w
B. ½ w
C. w
D. 2w
E. 4w

14. A heavy rod of length L and weight W is suspended horizontally by two vertical ropes as shown on the right. The first rope is attached to the left end of the rod while the second rope is attached a distance ¼ L from the right end.

PO1995ques14diagram.gif (1433 bytes)

The tension in the second rope is:

A. ¹/₂ W
B. ¹/₄ W
C. ¹/₃ W
D. ²/₃ W
E. W

15. A block of ice with mass m falls into a lake. After impact, a mass of ice m/5 melts. Both the block of ice and the lake have a temperature of 0º C. If L represents the heat of fusion, the minimum distance the ice fell is:

16. Which of the accompanying PV diagrams best represents an isothermal (constant temperature) process?

PO1995ques16ans.gif (2644 bytes)

17. If the heat is added at constant volume, 6300 joules of heat are required to raise the temperature of an ideal gas by 150 K. If instead, the heat is added at constant pressure, 8800 joules are needed for the same temperature change. When the temperature of the gas changes by 150 K, the internal energy of the gas changes by:

A. 2500 J
B. 6300 J
C. 8800 J
D. 11,300 J
E. 15,100 J

18. A firecracker exploding on the surface of a lake is heard as two sounds – a time interval t apart – by the paddler of a nearby canoe. Sound travels with a speed u in water and a speed v in air. The distance from the exploding firecracker to the canoe is:

19. Two interfering waves have the same wavelength, frequency, and amplitude. They are traveling in the same direction but are 90º out of phase. Compared to the individual waves, the resultant wave will have the same:

A. amplitude and velocity but different wavelength.
B. amplitude and wavelength but different velocity.
C. wavelength and velocity but different amplitude.
D. amplitude and frequency but different velocity.
E. frequency and velocity but different wavelength.

20. An organ pipe which is open at both ends resonates with fundamental frequency 300 Hz. If one end of the pipe is closed, it will resonate with a fundamental frequency of:

A. 75 Hz
B. 150 Hz
C. 300 Hz
D. 600 Hz
E. 1200 Hz