# Physics for the Life Sciences, PHYS*1080 - Sample Exam 1

1. A boy throws a stone from the edge of a cliff with an initial speed $\mathrm {v_o}$ at an angle of $30^\circ$ above the horizontal. When it hits the surface of a lake 22 m below the top of the cliff, the stone is moving with speed 25 m/s. What was its initial speed $\mathrm {v_o}$?

(A) 10 m/s
(B) 14 m/s
(C) 35 m/s
(D) 90 m/s
(E) 17 m/s

2. A car of mass 3500 kg is initially moving at 60 km/hr. On applying the brakes, the car comes to rest in a distance of 44 m. What is the average friction force between the car's tires and the road?

(A) $\mathrm {205 \;N}$
(B) $\mathrm {4.6 \times 103\; N}$
(C) $\mathrm {1.1 \times 104\; N}$
(D) $\mathrm {3.3 \times 104\; N}$
(E) $\mathrm {5.2 \times 105 \;N}$

3. A swimmer swims at a speed of 2.5 m/s in still water. She wants to swim straight across the river from south to north, but the river is flowing from east to west with a speed of 2.0 m/s. In order to swim straight across the river, in which direction should she head?

(A) $\mathrm {53^\circ\; north\;of \;east }$
(B) $\mathrm {32^\circ \;east\; of\; north}$
(C) $\mathrm {32^\circ \;west \;of \;north}$
(D) $\mathrm{41^\circ \; east \;of \;north}$
(E) $\mathrm {37 ^\circ \; north \;of \;east}$

4. The uniform beam AB is pivoted at A and has a mass of 50 kg. The rope from C to the wall is fastened at the midpoint of AB. What is the tension in the rope when a 800 N weight is suspended from B? (A) 1260 N
(B) 1500 N
(C) 900 N
(D) 1620 N
(E) 1800N

5. A figure skater is initially spinning with her arms extended. Shen then draws in her arms, decreasing her moment of inertia by 30%. Only one of the following statements is correct. Which one?

(A)    Her angular momentum increases by 43% and her angular velocity is unchanged.
(B)    Her rotational kinetic energy increases by 29% and her angular momentum is unchanged.
(C)    Her angular velocity increases by 29% and her angular momentum is unchanged.
(D)    Her angular velocity and rotational kinetic energy both increase by 43%.
(E)    Her angular velocity increases by 43 % and her rotational kinetic energy increases by 29 % .

6. Two bones, one hollow and one solid, have the same shear modulus and the same length. The hollow bone has an outer radius of 2.00 cm and an inner radius of 1.40 cm. The radius of the solid bone is 1.85 cm. Determine the ratio:

$\mathrm {\frac {Torque\; required \;to \;twist\; the \;hollow \;bone\; by\; 1^\circ}{ Torque\; required \;to \;twist \;the \;solid \;bone \;by\; 1^\circ} }$

(A) 1.41
(B) 1.01
(C) 0.87
(D) 0.52
(E) 0.26

7. A weightlifter having body mass 54 kg can lift 145 kg. According to scaling theory, how much mass should a weightlifter of body mass 84 kg be able to lift?The answers are expressed to the nearest kilogram.

(A) 205 kg
(B) 161 kg
(C) 195 kg
(D) 182 kg
(E) 171 kg

8. A woman of mass 50 kg is doing pushups. During each pushup, she raises her centre of mass a distance of 0.30 m. How much food energy is required for her to do 15 pushups? (This is the energy over and above that required for her to rest for an equal time. Assume that 4.0 units of food energy are required for 1.0 unit of usable energy.)

(A) $\mathrm {3.4\; J}$
(B) $\mathrm {1.8 \times 102 \;J}$
(C) $\mathrm {2.6 \times 103\; J}$
(D) $\mathrm {8.8 \times 103 \;J}$
(E) $\mathrm {1.5 \times 104 \;J}$

9. What gauge pressure $\mathrm {P_g}$ must be applied to the tube in order to produce bubbles in water at the fine tip (of radius 1.0 mm) immersed 2.0 cm below the water surface? (A)    150 Pa
(B)    203 Pa
(C)    336 Pa
(D)    398 Pa
(E)    476 Pa

10. How much work is done to blow a soap bubble in air from an initial volume of 8.0 $\mathrm {cm^3}$ to a final volume of 27.0 $\mathrm {cm^3}.$ The surface tension of the soap solution is 0.015 N/m.

(A)    $\mathrm {7.25 \times 10^{-5}\; J}$
(B)    $\mathrm {1.15 \times 10^{-4}\; J}$
(C)    $\mathrm{2.30 \times 10^{-4}\; J}$
(D)    $\mathrm {5.77 \times 10^{-3}\; J}$
(E)    $\mathrm {0.023\; J}$

11. In the following diagram, water is flowing from left to right. The radius of the tube on the left is 8.0 mm while on the right it is 4.0 mm. The flow speed on the left side is 15 cm/s and the gauge pressure there is 1500 Pa. What is the gauge pressure on the right? Water can be treated as an ideal fluid in this situation. (A) $\mathrm{1.5 \times 10^2 \;Pa }$
(B) $\mathrm {3.5 \times 10^2 \;Pa }$
(C) $\mathrm {5.5 \times 10^2\; Pa}$
(D) $\mathrm {7.5 \times 10^2\; Pa}$
(E) $\mathrm {9.5 \times 10^2 \;Pa}$

12. Suppose a diseased artery has a cross-sectional area which is only 40% of what it was when it was healthy. For the same pressure gradient, what fraction of the original flow rate can it now carry?
(A) 0.16
(B) 0.26
(C) 0.36
(D) 0.46
(E) 0.56

13. For incompressible fluids, the continuity equation can be used

(A) only for streamline flow
(B) only for turbulent flow
(C) only for bolus flow
(D) only for pulsatile flow
(E) for all of the above-mentioned types of flow

14. For the flow rate vs. time graph shown below, there is a flow of $\mathrm {1.5\; cm^3}$ with each beat of the heart. If there are 1.2 beats per second, what is the maximum Reynolds number? The viscosity of blood is $\mathrm {4.5 \times 10^{-3} N\; s\; m^{-2}}$ and the diameter of the blood vessel is 1.0 cm. (A) $\mathrm {5.0 \times 10^1}$
(B) $\mathrm {1.0 \times 10^2 }$
(C) $\mathrm {1.5 \times 10^2}$
(D) $\mathrm {2.0 \times 10^2}$
(E) $\mathrm {2.5 \times 10^2}$

15. How far above sea level would you have to be for the atmospheric pressure to be 25% of the sea level pressure? Let the molar mass of air be 29 grams per mole and the temperature be 20° C.

(A) 3.0 km
(B) 6.0 km
(C) 9.0 km
(D) 12 km
(E) 15 km

16. A biophysicist wants to separate white blood cells from the water in which they are uniformly suspended. The density of the cells is $\mathrm {1.0015 \times 10^3\; kg\; m^{-3}}$ and their average radius is $\mathrm {5.0 \times 10^{-6} m.}$ The researcher fills a graduated test tube to a depth of 0.025 m with the very dilute suspension and starts the centrifuge spinning at 2000 revolutions per minute. The cells have all reached the bottom at the end of a 500- second interval. What is the radius of the centrifuge?

(A) 12 cm
(B) 14 cm
(C) 16 cm
(D) 18 cm
(E) 20 cm

17. While digging in the garden, you turn up an ant nest and observe them go into completely random motion over the ground. After 20 seconds, $\frac {1}{3}$ of them are at least 15 cm from the starting point. How far would $\frac {1}{3}$ of them be after another 10 seconds?

(A) 18 cm
(B) 22 cm
(C) 26 cm
(D) 30 cm
(E) 34 cm

18. An erythrocyte for which 0.15 Molar NaCl is isotonic is placed in a solution which is a mixture of 0.13 Molar NaCl and 0.13 Molar glycerol. The cell

(A) shrinks by 30%
(B) shrinks by 15%
(C) neither shrinks nor swells
(D) swells by 15%
(E) swells by 30%

19. A window of area $\mathrm {5.0\; m^2}$ loses heat to the outside at a rate of 5000 watts. The thermal conductivity of glass is $\mathrm {0.80 \;W \;m^{-1} K^{-1}}.$ The inside surface is $\mathrm {5.0 \;^{\circ}C}$ warmer than the outside surface. What is the thickness of the glass?

(A) 1.6 mm
(B) 2.4 mm
(C) 3.2 mm
(D) 4.0 mm
(E) 4.8 mm

20. An object is cooling off according to Newton's law of cooling. Initially it is at 70° C. 5.0 minutes later it is at 50° C. 5.0 minutes after that it is at 38° C. What is the temperature of the surroundings?

(A) 16° C
(B) 20° C
(C) 24° C
(D) 28° C
(E) 32° C

1. B
2. C
3. E
4. A
5. D
6. B
7. C
8. D
9. C
10. A
11. C
12. A
13. E
14. D
15. D
16. B
17. A
18. D
19. D
20. B