ASVAB Mechanical Comprehension Practice Test 705292 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.00
Score	0%	60%

Review

1 70 lbs. of effort is used by a machine to lift a 420 lbs. box. What is the mechanical advantage of the machine?

84% Answer Correctly

	12
	6
	2
	6.6

Solution

Mechanical advantage is resistance force divided by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{420 lbs.}{70 lbs.} \) = 6

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

48% Answer Correctly

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

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.

Sam can do 50 ft. lb. of work in 2 minutes and 5 seconds. What would Sam have to do to increase his power output?

64% Answer Correctly

	do 25 ft. lb. of work in 2 minutes 5 seconds
	do the work in 3 minutes
	do 100 ft. lb. of work in 4 minutes 12 seconds
	do the work in 2 minutes

Solution

Power is the rate of doing work or \(\frac{W}{t}\). To increase power, increase the work being done in the same amount of time or do the same amount of work in less time.

Which of the following statements about drag is false?

58% Answer Correctly

	slower objects experience more drag than faster objects
	the amount of drag depends on the speed of an object
	drag occurs during movement through a fluid
	the amount of drag depends on the shape of an object

Solution

Drag is friction that opposes movement through a fluid like liquid or air. The amount of drag depends on the shape and speed of the object with slower objects experiencing less drag than faster objects and more aerodynamic objects experiencing less drag than those with a large leading surface area.

5 If the handles of a wheelbarrow are 2.5 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 190 lbs. force lift?

47% Answer Correctly

	-56
	655.4
	475
	190

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:
\( F_r = \frac{F_e d_e}{d_r} \)
\( F_r = \frac{190 \times 2.5}{1.0} \)
\( F_r = \frac{475.0}{1.0} \)
\( F_r = 475 \)