ASVAB Mechanical Comprehension Practice Test 803090 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.27
Score	0%	65%

Review

Which of the following surfaces would have the highest coefficient of friction?

77% Answer Correctly

	marble
	concrete
	steel
	ice

Solution

Coefficient of friction (μ) represents how much two materials resist sliding across each other. Smooth surfaces like ice have low coefficients of friction while rough surfaces like concrete have high μ.

A box is resting on a smooth floor. Static friction is present:

59% Answer Correctly

	when an attempt is made to move the box
	only if normal force is present
	if the coefficient of friction is greater than one
	at all times

Solution

For any given surface, the coefficient of static friction is higher than the coefficient of kinetic friction. More force is required to initally get an object moving than is required to keep it moving. Additionally, static friction only arises in response to an attempt to move an object (overcome the normal force between it and the surface).

3 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 140 lbs. force lift?

47% Answer Correctly

	280
	None of these is correct
	70
	-39

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:
\( F_r = \frac{F_e d_e}{d_r} \)
\( F_r = \frac{140 \times 0.5}{1.0} \)
\( F_r = \frac{70.0}{1.0} \)
\( F_r = 70 \)

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

61% Answer Correctly

	increase, increase
	increase, decrease
	decrease, 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.

5 What is the mechanical advantage of this inclined plane if the length of the ramp is 30 ft. and the height of the green box is 5 ft.?

82% Answer Correctly

	12
	6
	7.5
	2

Solution

The mechanical advantage (MA) of an inclined plane is the effort distance divided by the resistance distance. In this case, the effort distance is the length of the ramp and the resistance distance is the height of the green box:

MA = \( \frac{d_e}{d_r} \) = \( \frac{30 ft.}{5 ft.} \) = 6