Question

# 1. A person pushes on a doorknob with a force of 5.00 N perpendicular to the...

1. A person pushes on a doorknob with a force of 5.00 N perpendicular to the surface of the door. The doorknob is located 0.800 m from the axis of the hinges of the door. The door begins to rotate with an angular acceleration of 2.00 rad/s2. What is the moment of inertia of the door about hinges?

Select one:

a. 6.50 kg.m2

b. 2.50 kg.m2

c. 12.5 kg.m2

d. 2.00 kg.m2

2. A dumbbell has a connecting bar of negligible mass. Find the location of its center of mass (XCM) if the end masses m1 and m2 are 5.0 kg and 10.0 Kg, respectively. m1 is located at 0.20 m and m2 is located at 0.90 m on the x-axis.

Select one:

a. 0.67 m

b. 0.55 m

c. 0.61 m

d. 0.30 m

3.A crane lifts the 16,000-kg steel hull of a sunken ship out of the water. Determine the tension in the crane’s cable when the hull is fully submerged in water. Density of water = 1000 kg/m3. Density of steel = 7800 kg/m3.

Select one:

a. 6.4 X 105 N

b. 1.4 X 103 N

c. 1.4 X 105 N

d. 2.4 X 105 N

4.Three loops are observed on a string fixed at both ends as it vibrates at a frequency of 180 Hz. The fundamental frequency of the string is

Select one:

a. 30 Hz

b. 20 Hz

c. 90 Hz

d. 60 Hz

5.A golfer drives a 0.046 kg ball from an elevated tee, giving the ball a horizontal speed of 40.0 m/s. If the during of contact is 1.00 X 10–3 s, what is the magnitude of the average force exerted by the club on the ball during this time?

Select one:

a. 7800 N

b. 3800 N

c. 1840 N

d. 1200 N

6.An object of mass 2.00 kg starts at rest from the top of a smooth inclined plane (no friction) of height 20.0 m. What is the speed of the object as it reaches the bottom of the inclined plane?

Select one:

a. 15.6 m/s

b. 19.8 m/s

c. 12.4 m/s

d. 17.1 m/s

7.A man is holding an 8.00-kg vacuum cleaner at arm’s length, a distance of 0.550 m from the shoulder. What is the torque on the shoulder joint if the arm is horizontal?

Select one:

a. 14.5 N.m

b. 4.40 N.m

c. 0.242 N.m

d. 43.1 N.m

(1) Moment of force, T = 5.0 * 0.8 = 4.0 N*m

Suppose,

I = Moment of inertia of the door about the hinges.

= angular acceleration = 2.0 rad/s^2

Now -

T = I*

=> I = T / = 4.0 / 2.0 = 2.0 kg*m^2

Hence, option (d) is the correct answer.

(2) Center of mass = (m1*r1 + m2*r2) / (m1 + m2) = (5*0.2 + 10*0.9) / (5 + 10) = (1.0 + 9.0) / 15 = 0.67 m

Hence, option (a) is the correct answer.

(3) Volume of the steel hull, V = 16000 / 7800 m^3 = 2.05 m^3

So,

Tension in the crane's cable, T = m*g - V*1000*g

= 16000*9.8 - 2.05*1000*9.8

= 156800 - 20090 = 136710 N = 1.4 x 10^5 N

Hence, option (c) is the correct answer.

(4) Fundamental frequency = 180 / 3 = 60 Hz

Hence, option (d) is the correct answer.

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