Exercise list 1. Biophysics. Prof.
Helman Amaya
Name___________________________________
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) The following exact conversion equivalents are given: 1 m = 100 cm , 1 in = 2.54 cm, and 1)
1 ft = 12 in. If a computer screen has an area of 1.27 ft2 , this area is closest to
A) 4.65 m2 .
B) 0.0465 m2 .
C) 0.284 m2 .
D) 0.00284 m2 .
E) 0.118 m2 .
2) An apple falls from an apple tree growing on a 20° slope. The apple hits the ground with an impact 2)
velocity of 16.2 m/s straight downward. What is the component of the apple's impact velocity
parallel to the surface of the slope?
A) 5.5 m/s B) 15 m/s C) 12 m/s D) 8.7 m/s
3) A rabbit trying to escape a fox runs north for 8.0 m, darts northwest for 1.0 m, then drops 1.0 m 3)
down a hole into its burrow. What is the magnitude of the net displacement of the rabbit?
A) 10 m B) 8.1 m C) 66 m D) 8.8 m
4) Three forces are exerted on an object placed on a tilted floor. Forces are vectors. The three forces are 4)
directed as shown in the figure. If the forces have magnitudes F1 = 1.0 N, F2 = 8.0 N and F3 = 7.0
N, where N is the standard unit of force, what is the component of the net force F net = F 1 + F 2 +
F 3 parallel to the floor?
A) 6.0 N B) 7.8 N C) 2.5 N D) 5.1 N
5) A lever is 5.0 m long. The distance from the fulcrum to the weight to be lifted is 1.0 m. If a worker 5)
pushes on the opposite end with 400 N, what is the maximum weight that can be lifted?
A) 1600 N B) 2000 N C) 100 N D) 80 N
6) A boy and a girl are balanced on a massless seesaw. The boy has a mass of 75 kg and the girl's 6)
mass is 50 kg. If the boy sits 2.0 m from the pivot point on one side of the seesaw, where must the
girl sit on the other side?
A) 2.3 m B) 2.5 m C) 3.0 m D) 1.3 m
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FIGURE 12-8
7) A stepladder consists of two halves, hinged at the top, and connected by a tie rod which keeps the 7)
two halves from spreading apart. In this particular instance, the two halves are 2.50 m long, the tie
rod is connected to the center of each half and is 70.0 cm long. An 800-N person stands 3/5 of the
way up the stepladder, as shown in Figure 12-8. Neglecting the weight of the ladder, and
assuming that the ladder is resting on a smooth floor, what is the tension in the tie rod? Note: to
solve this problem you must "cut" the ladder in half and consider the equilibrium of forces and
torques acting on each half of the ladder.
A) 140 N B) 560 N C) 240 N D) 280 N E) 360 N
8) An athlete holds a 7.5-kg shot put in his hand with his lower arm horizontal, as shown in the 8)
figure. His lower arm has a mass of 2.8 kg and its center of gravity (or center of mass) is 12 cm from
the elbow-joint pivot. How much force must the extensor muscle (which is F M in the figure) in the
upper arm exert on the lower arm?
A) 1500 N B) 100 N C) 500 N D) 1000 N
9) What is the spring constant of a spring that stretches 2.00 cm when a mass of 0.600 kg is suspended 9)
from it?
A) 294 N/m B) 2.94 N/m C) 0.300 N/m D) 30.0 N/m
10) A mass is attached to a spring of spring constant 60 N/m along a horizontal, frictionless surface. 10)
The spring is initially stretched by a force of 5.0 N on the mass and let go. It takes the mass 0.50 s
to go back to its equilibrium position when it is oscillating. What is the frequency of oscillation?
A) 1.5 Hz B) 0.50 Hz C) 2.0 Hz D) 1.0 Hz
11) Suppose that an 80-kg person walking on crutches supports all his weight on the two crutch tips, 11)
each of which is circular with a diameter of 4.0 cm. What pressure is exerted on the floor?
A) 78 kPa B) 156 kPa C) 624 kPa D) 312 kPa
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12) A bridge piling has an area of 1.250 m2 . It supports 1875 N. Find the stress on the column. 12)
A) 2344 N/m2 B) 1875 N/m2 C) 1500 N/m2 D) 1875 N
13) A 55-cm brass rod has a diameter of 30 cm. The compressive strength of steel is 250 × 10 6 N/m 2 . 13)
What is the compression force that would break the rod?
A) 2.4 × 108 N B) 1.4 × 108 N C) 1.8 × 107 N D) 4.5 × 108 N
14) A steel lift column in a service station is a solid cylinder 4.0 m long and 0.20 m in diameter. 14)
Young's modulus for this steel is 20 × 1010 N/m2 . By what distance does the column compress
when a 5000-kg truck is on it?
A) 3.2 × 10-6 m
B) 4.7 × 10-7 m
C) 3.1 × 10-5 m
D) 8.0 × 10-7 m
E) 7.8 × 10-6 m
15) A cable is 100-m long and has a cross-sectional area of 1 mm2 . A 1000-N force is applied to 15)
stretch the cable. The elastic modulus for the cable is 1.0 × 1011 N/m2 . How far does it stretch?
A) 0.01 m B) 10 m C) 1.0 m D) 0.10 m
