Asvab Mechanical Comprehension

Front 1

If the speed of a stone tied to the end of a string swinging in a circular motion is tripled, how will the centripetal force of the stone be affected?

Back 1

It will increase by 9X because the centripetal force of the stone is proportional to the square of the velocity.

Front 2

Which of the following units measures the weight of a body?

A. pound
B. Newton
C. kilogram
D. kg.m/s2

Back 2

B. Newton (because the weight of a body is a force, and newton is the unit of force).

Front 3

What is the unit of work, kinetic energy, potential energy, and heat?

Back 3

The joule.

Front 4

Why would two objects with different weights, if dropped at the same moment from the top of the Leaning Tower of Pisa, both hit the ground at the same time?

Back 4

The travel time depends on the height above ground and the acceleration of gravity, both of which are the same for both objects.

Front 5

Of what is the quantity 2 m/s2 a measure?

Back 5

ACCELERATION. (The quantity 2 m/s2 can be thought of as 2 m/s per second; that is, speed per unit time, or acceleration).

Front 6

How does Newton's 2nd Law of motion explain why the acceleration of a car moving around a circular track at a constant speed, is towards the center of the circle.

Back 6

Newton's 2nd law of motion: the centripetal force, or the inward force necessary to maintain uniform circular motion, is the product of mass and centripetal acceleration.

Front 7

A ball thrown vertically upward has an initial potential energy of 100 J and an initial kinetic energy of 700 J. Why, at the top of the trajectory, is its energy in joules 800 J?

Back 7

At the top of the trajectory the ball stops and all the kinetic energy has already been converted to potential energy. Thus the total energy is the sum of 100 and 700, or 800 J.

Front 8

A simple pendulum has a frequency of oscillation f. Why must the length of the pendulum be decreased by a factor of 4 in order to double f?

Back 8

Since the frequency of oscillation is inversely proportional to the square root of the length of the pendulum, the length has to be decreased by a factor of 4 for the frequency to be doubled.

Front 9

What is the velocity of a baseball 4 seconds after it is thrown vertically upward with a speed of 32.1 m/s?

Back 9

initial VEL - 4(9.8 m/s) = final VEL (after 4 s):
The final velocity is the initial velocity minus four times the acceleration of gravity (9.8 m/s) or -7.14 (about 7.2) m/s

Front 10

Why must a volleyball player's initial velocity be 3.92 m/s in order for him to jump vertically 0.8 m?

Back 10

Using the expressions s=vot +1/2at2 and vf = vo + at , you obtain = 0.4 s and vo = 3.92 m/s.

Front 11

Explain why the graph of velocity versus time for an object with a constant negative acceleration would be a straight line with a negative slope.

Back 11

The slope has to be constant and must also be negative since the acceleration is constant and negative, and acceleration is the time derivative of the velocity.

Front 12

Since the torque T = Fd cos q where F is the force, d is the arm, and q is the angle between the force and arm, then you can solve for F to obtain an answer in N.

Back 12

Cos (of an angle)= ratio of adjacent length to hypoteneuse length (a/h) ***sec = h/a (inverse)****

Front 13

Define sin (cosec), cos (sec), and tan (ctn),

Back 13

o/h(h/o)***a/h (h/a)***o/a (a/o)

Front 14

In the spur gear arrangement shown in the figure, the ratio of the number of teeth on the output gear (No) to the number of teeth on the input gear (Ni) is 2. EXPLAIN WHY the speed ratio of the input and output gears is 2.

Back 14

The speed ratio of input to output gears equals the mechanical advantage, which is the ratio No/Ni, or 2.

Front 15

What is the speed of a baseball with a momentum of 5.8 kilograms m/s and a mass of 0.145 kilograms?

Back 15

40 m/s BECAUSE momentum (P) = mass (m) X velocity (v), it follows that v = P/m = 40.00 m/s.

Front 16

A 0.24-kilogram glider moving with a velocity of 0.6 m/s collides with and sticks to a 0.26-kilogram glider moving with a velocity of 0.2 m/s. The final velocity v of the two gliders is 0.392 m/s. Why?

Back 16

Conservation of momentum requires that 0.24(0.6) + 0.26(0.2) = (0.24 + 0.26)v. Hence v = 0.392 m/s.

Front 17

A massless, horizontal, rigid rod of length 3d is pivoted at a fixed point W, and two forces each of magnitude F are applied vertically upward as shown in the figure. In order to achieve rod equilibrium, a third vertical force of magnitude F is to be applied at which of the labeled points? OPT: v, w, x, y

Back 17

A: V (UPWARD F) OR X (DOWNWARD F) ONLY. For rod equilibrium the clockwise and counterclockwise torques must be equal, i.e., (F at V + F at V)(d) = (F at Y) (2d) or (F at V)D = (F at Y) (2d) - (F at X)D, which means that the third force can only be applied upward at V or downward at X.

Front 18

Two balls of different masses are thrown vertically up from the same point and at the same time. The two balls will experience the same change in
velocity, not acceleration, energy, or momentum.

Back 18

Acceleration will be the same for both arrows. Momentum and energy are dependent on mass and will therefore be different. Only the change in velocity will be the same for both arrows.

Front 19

As an arrow shot vertically upwards approaches its maximum altitude, why does the amount of work done against gravity remain the same?

Back 19

The work done does not depend on time or path of travel since the deceleration of the arrow is constant.

Front 20

What determines the resistance of an object to a change of motion?

Back 20

THE OBJECT'S MASS. (The resistance to motion is a force that is determined by mass in accordance with Newton's second law).