ASVAB Mechanical Comprehension Practice Test 915555 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.23
Score	0%	65%

Review

1 What is the efficiency of a machine has work input of 80 ft⋅lb and work output of 32 ft⋅lb?

67% Answer Correctly

	80%
	0%
	40%
	60%

Solution

Due to friction, a machine will never be able to utilize 100% of its work input. A certain percentage of that input will be lost in overcoming friction within the machine. Effeciency is a measure of how much of a machine's work input can be turned into useful work output and is calculated by dividing work output by work input and multiplying the result by 100:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{32 ft⋅lb}{80 ft⋅lb} \times 100 \) \( = 40% \) %

2 If the handles of a wheelbarrow are 0.5 ft. from the wheel axle, how many pounds of force must you exert to lift the handles if it's carrying a 170 lbs. load concentrated at a point 1.0 ft. from the axle?

52% Answer Correctly

	97.1
	340
	None of these is correct
	69

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 effort force:
\( F_e = \frac{F_r d_r}{d_e} \)
\( F_e = \frac{170 \times 1.0}{0.5} \)
\( F_e = \frac{170.0}{0.5} \)
\( F_e = 340 \)

Which of these is the formula for kinetic energy?

67% Answer Correctly

	\(KE = {m \over v^2 }\)
	\(KE = mgh\)
	\(KE = {1 \over 2}mv^2\)
	\(KE = {1 \over 2}mh^2\)

Solution

Kinetic energy is the energy of movement and is a function of the mass of an object and its speed: \(KE = {1 \over 2}mv^2\) where m is mass in kilograms, v is speed in meters per second, and KE is in joules. The most impactful quantity to kinetic energy is velocity as an increase in mass increases KE linearly while an increase in speed increases KE exponentially.

The force exerted on an object due to gravity is called:

70% Answer Correctly

	density
	mass
	weight
	potential energy

Solution

Mass is an intrinsic property of matter and does not vary. Weight is the force exerted on the mass of an object due to gravity and a specific case of Newton's Second Law of Motion. Replace force with weight and acceleration with acceleration due to gravity on Earth (g) and the result is the formula for weight: W = mg or, substituting for g, weight equals mass multiplied by 9.8 m/s².

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 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.