ASVAB Mechanical Comprehension Practice Test 926692 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.05
Score	0%	61%

Review

Power is the rate at which:

62% Answer Correctly

	friction is overcome
	work is done
	potential energy is converted into kinetic energy
	input force is transferred to output force

Solution

Power is the rate at which work is done, P = w/t, or work per unit time. The watt (W) is the unit for power and is equal to 1 joule (or newton-meter) per second. Horsepower (hp) is another familiar unit of power used primarily for rating internal combustion engines. 1 hp equals 746 watts.

2 The radius of the axle is 3, the radius of the wheel is 6, and the blue box weighs 40 lbs. What is the effort force necessary to balance the load?

53% Answer Correctly

	8 lbs.
	20 lbs.
	12 lbs.
	6 lbs.

Solution

The mechanical advantage of a wheel and axle is the input radius divided by the output radius:

MA = \( \frac{r_i}{r_o} \)

In this case, the input radius (where the effort force is being applied) is 6 and the output radius (where the resistance is being applied) is 3 for a mechanical advantage of \( \frac{6}{3} \) = 2.0

MA = \( \frac{load}{effort} \) so effort = \( \frac{load}{MA} \) = \( \frac{40 lbs.}{2.0} \) = 20 lbs.

3 If the green arrow in this diagram represents 800 ft⋅lb of work, how far will the box move if it weighs 160 pounds?

72% Answer Correctly

	5 ft.
	640 ft.
	10 ft.
	2 ft.

Solution

The Law of Work states that the work put into a machine is equal to the work received from the machine under ideal conditions. In equation form, that's:

W_in = W_out
F_effort x d_effort = F_resistance x d_resistance

In this problem, the effort work is 800 ft⋅lb and the resistance force is 160 lbs. and we need to calculate the resistance distance:

W_in = F_resistance x d_resistance
800 ft⋅lb = 160 lbs. x d_resistance
d_resistance = \( \frac{800ft⋅lb}{160 lbs.} \) = 5 ft.

A box is resting on a smooth floor. Static friction is present:

59% Answer Correctly

	when an attempt is made to move the box
	at all times
	only if normal force is present
	if the coefficient of friction is greater than one

Solution

For any given surface, the coefficient of static friction is higher than the coefficient of kinetic friction. More force is required to initally get an object moving than is required to keep it moving. Additionally, static friction only arises in response to an attempt to move an object (overcome the normal force between it and the surface).

Which of the following will increase the mechanical advantage of this inclined plane?

59% Answer Correctly

	lengthen the ramp
	shorten the ramp
	lower the force acting at the blue arrow
	increase the force acting at the blue arrow

Solution

The mechanical advantage (MA) of an inclined plane is the effort distance divided by the resistance distance. In order to increase mechanical advantage, this ratio must increase which means making the effort distance longer and this can be accomplished by lengthening the length of the ramp.