ASVAB Mechanical Comprehension Practice Test 974541 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.31
Score	0%	66%

Review

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?

63% Answer Correctly

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

2 60 lbs. of effort is used by a machine to lift a 180 lbs. box. What is the mechanical advantage of the machine?

84% Answer Correctly

	-2
	3
	12
	4.5

Solution

Mechanical advantage is resistance force divided by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{180 lbs.}{60 lbs.} \) = 3

Two gears are connected and the larger gear drives the smaller gear. The speed of rotation will __________ and the torque will __________.

61% Answer Correctly

	decrease, decrease
	increase, increase
	increase, decrease
	decrease, increase

Solution

Connected gears of different numbers of teeth are used together to change the rotational speed and torque of the input force. If the smaller gear drives the larger gear, the speed of rotation will be reduced and the torque will increase. If the larger gear drives the smaller gear, the speed of rotation will increase and the torque will be reduced.

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

84% Answer Correctly

	wedge
	none of these
	first-class lever
	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.

5 What is the power output of a 6 hp engine that's 25% efficient?

40% Answer Correctly

	4 \( \frac{ft⋅lb}{s} \)
	825 \( \frac{ft⋅lb}{s} \)
	2475 \( \frac{ft⋅lb}{s} \)
	3300 \( \frac{ft⋅lb}{s} \)

Solution

\( Efficiency = \frac{Power_{out}}{Power_{in}} \times 100 \)
Solving for power out: \( P_{o} = \frac{E \times P_{i}}{100} \)
Knowing that 1 hp = 550 \( \frac{ft⋅lb}{s} \), P_i becomes 6 hp x 550 \( \frac{ft⋅lb}{s} \) = 3300 \( \frac{ft⋅lb}{s} \)
\( P_{o} = \frac{E \times P_{i}}{100} = \frac{25 \times 3300 \frac{ft⋅lb}{s}}{100} \) \( = \frac{82500 \frac{ft⋅lb}{s}}{100} \) = 825 \( \frac{ft⋅lb}{s} \)