ASVAB Mechanical Comprehension Practice Test 63325 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.14
Score	0%	63%

Review

1 If the handles of a wheelbarrow are 0.5 ft. from the wheel axle and the load is concentrated at a point 1.0 ft. from the axle, how many pounds of load will a 200 lbs. force lift?

47% Answer Correctly

	None of these is correct
	-20.3
	100
	108.3

Solution

This problem describes a second-class lever and, for a second class lever, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance: F_ed_e = F_rd_r. In this problem we're looking for resistance force:
\( F_r = \frac{F_e d_e}{d_r} \)
\( F_r = \frac{200 \times 0.5}{1.0} \)
\( F_r = \frac{100.0}{1.0} \)
\( F_r = 100 \)

2 If a 50 lbs. weight is placed 5 ft. from the fulcrum at the blue arrow and the green box is 8 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?

61% Answer Correctly

	0 lbs.
	31.25 lbs.
	250 lbs.
	15.63 lbs.

Solution

To balance this lever the torques on each side of the fulcrum must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

R_ad_a = R_bd_b

where a represents the left side of the fulcrum and b the right, R is resistance (weight) and d is the distance from the fulcrum.

Solving for R_a, our missing value, and plugging in our variables yields:

R_a = \( \frac{R_bd_b}{d_a} \) = \( \frac{50 lbs. \times 5 ft.}{8 ft.} \) = \( \frac{250 ft⋅lb}{8 ft.} \) = 31.25 lbs.

A ramp is an example of which kind of simple machine?

84% Answer Correctly

	first-class lever
	wedge
	none of these
	inclined plane

Solution

An inclined plane is a simple machine that reduces the force needed to raise an object to a certain height. Work equals force x distance and, by increasing the distance that the object travels, an inclined plane reduces the force necessary to raise it to a particular height. In this case, the mechanical advantage is to make the task easier. An example of an inclined plane is a ramp.

4 If the green arrow in this diagram represents 400 ft⋅lb of work, how far will the box move if it weighs 80 pounds?

72% Answer Correctly

	10 ft.
	20 ft.
	2 ft.
	5 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 400 ft⋅lb and the resistance force is 80 lbs. and we need to calculate the resistance distance:

W_in = F_resistance x d_resistance
400 ft⋅lb = 80 lbs. x d_resistance
d_resistance = \( \frac{400ft⋅lb}{80 lbs.} \) = 5 ft.

Which of the following statements about this pulley configuration is false?

48% Answer Correctly

	This is a block and tackle pulley configuration
	Only multiplies the effort force
	Changes the direction of and multiplies the effort force
	Mechanical advantage is the number of ropes that support the resistance

Solution

A block and tackle is a combination of one or more fixed pulleys and one or more movable pulleys where the fixed pulleys change the direction of the effort force and the movable pulleys multiply it. The mechanical advantage is equal to the number of times the effort force changes direction and can be increased by adding more pulley wheels to the system. An easy way to find the mechanical advantage of a block and tackle pulley system is to count the number of ropes that support the resistance.