ASVAB Mechanical Comprehension Practice Test 727971 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.17
Score	0%	63%

Review

The force amplification achieved by using a tool, mechanical device or machine system is called:

80% Answer Correctly

	work
	power
	mechanical advantage
	efficiency

Solution

Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. Such a device utilizes input force and trades off forces against movement to amplify and/or change its direction.

2 How much resistance could a 105 lb. effort force lift using a block and tackle pulley that has 10 ropes supporting the resistance?

81% Answer Correctly

	350 lbs.
	2100 lbs.
	1575 lbs.
	1050 lbs.

Solution

The mechanical advantage (MA) of a block and tackle pulley is equal to the number of times the effort force changes direction. An easy way to count how many times the effort force changes direction is to count the number of ropes that support the resistance which, in this problem, is 10. With a MA of 10, a 105 lbs. effort force could lift 105 lbs. x 10 = 1050 lbs. resistance.

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

48% Answer Correctly

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

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.

4 If the handles of a wheelbarrow are 1.5 ft. from the wheel axle and the load is concentrated at a point 1.5 ft. from the axle, how many pounds of load will a 110 lbs. force lift?

47% Answer Correctly

	None of these is correct
	42.8
	165
	110

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:
\( F_r = \frac{F_e d_e}{d_r} \)
\( F_r = \frac{110 \times 1.5}{1.5} \)
\( F_r = \frac{165.0}{1.5} \)
\( F_r = 110 \)

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

61% Answer Correctly

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

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.