A 4.0-kg mass is placed at (3.0, 4.0) m, and a 6.0-kg mass is placed at (3.0, -4

Question

A 4.0-kg mass is placed at (3.0, 4.0) m, and a 6.0-kg mass is placed at (3.0, -4.0) m. What is the moment of inertia of this system of masses about the x-axis? a. 160 kg middot m^2 b. 90 kg middot m^2 c. 250 kg middot m^2 d. 32 kg middot m^2 In a two-body collision, if the kinetic energy of the system is conserved, then which of the following best describes the momentum after the collision? a. must be less b. must also be conserved c. may also be conserved d. is doubled in value A bird, accelerating from rest at a constant rate, experiences a displacement of 28 m in 11 s. What is its acceleration? a. 0.21 m/s^2 b. 0.46 m/s^2 c. 0.64 m/s^2 d. 0.78 m/s^2 A truck moves 70 m east, then moves 120 m west, and finally moves east again a distance of 90 m. If east is chosen as the positive direction, what is the truck's resultant displacement? a. 40 m b. -40 m c. 280 m d. -280 m A ball is rolled horizontally off a table with an initial speed of 0.24 m/s. A stop watch measures the ball's trajectory time from table to the floor to be 0.30 s. How far away from the table does the ball land? (g = 9.8 m/s^2 and air resistance is negligible) a. 0.055 m b. 0.072 m c. 1.2 m d. 1.9 m 1 2 600 rav/min is equivalent to which of the following? a. 2600 rad/s b. 43.3 rad/s c. 273 rad/s d. 60 rad/s The position of a 0.64-kg mass undergoing simple harmonic motion is given by x = (0.160 m) cos (pi t/16). What is its position at t = 5.0 s? a. 0.160 m b. 0.159 m c. 0.113 m d. 0.089 m Doubling the tension in a guitar string will change its natural frequency by what factor? a. 0.71 b. 1.0 c. 1.4 d. 2.0 If both mass and velocity of a ball are tripled, the kinetic energy is increased by a factor of a. 3. b. 6. c. 9. d. 27. Find the tension in an elevator cable if the 1 000-kg elevator is descending with an acceleration of 1.8 m/s^2, downward. a. 5 700 N b. 8000 N c. 9800 N d. 11 600 N A meter stick is supported by a knife-edge at the 50-cm mark. Doug hangs masses of 0.40 and 0.60 kg from the 20-cm and 80 cm marks, respectively. Where should Doug hang a third mass of 0.30 kg to keep the stick balanced? a. 20 cm b. 70 cm c. 30 cm d. 25 cm

Explanation / Answer

10)

The moment of inertia is:

I = 4.0 * 3.0^2 + 6.0 * 3.0^2

I = 10 * 3^2

I = 90 kg m^2

11)

Ans - b) must also be conserved.

12)

The inital velocity is 0

Use this kinematic equation;

(distance) = 1/2 * (Vinitial)*(time) + (1/2)*(acceleration)* (time)^2

So, you have

(28m) = (1/2)(0)(11s) + (1/2)(A)(11^2)

28m = (0) + (60.5A)

A = 0.4628 m/s^2

13)

x = 70 - 120 + 90 = 40m

14)

As ball rolls of horizontal table, the initial vertical velocity is 0

h = ut + ½gt²
h = 0(0.30) + ½(9.81)(0.30)²
h = 0.44 m

15)

2600 rev/min = 273 rad/s

1 rad/s = 9.5493 rev/min

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