ASVAB Mechanical Comprehension Practice Test 756195 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.38
Score	0%	68%

Review

What type of load is sudden and for a relatively short duration?

69% Answer Correctly

	impact load
	concentrated load
	non-uniformly distributed load
	dynamic load

Solution

A concentrated load acts on a relatively small area of a structure, a static uniformly distributed load doesn't create specific stress points or vary with time, a dynamic load varies with time or affects a structure that experiences a high degree of movement, an impact load is sudden and for a relatively short duration and a non-uniformly distributed load creates different stresses at different locations on a structure.

2 If the green box is 7 ft. from the fulcrum and a certain force applied 2 ft. from the fulcrum at the blue arrow balances the lever, what is the mechanical advantage?

61% Answer Correctly

	7.29
	0.29
	0.31
	0.1

Solution

Because this lever is in equilibrium, we know that the effort force at the blue arrow is equal to the resistance weight of the green box. For a lever that's in equilibrium, one method of calculating mechanical advantage (MA) is to divide the length of the effort arm (E_a) by the length of the resistance arm (R_a):

MA = \( \frac{E_a}{R_a} \) = \( \frac{2 ft.}{7 ft.} \) = 0.29

When a lever is in equilibrium, the torque from the effort and the resistance are equal. The equation for equilibrium is R_ad_a = R_bd_b where a and b are the two points at which effort/resistance is being applied to the lever.

In this problem, R_a and R_b are such that the lever is in equilibrium meaning that some multiple of the weight of the green box is being applied at the blue arrow. For a lever, this multiple is a function of the ratio of the distances of the box and the arrow from the fulcrum. That's why, for a lever in equilibrium, only the distances from the fulcrum are necessary to calculate mechanical advantage.

If the lever were not in equilibrium, you would first have to calculate the forces and distances necessary to put it in equilibrium and then divide E_a by R_a to get the mechanical advantage.

3 If A = 9 ft., B = 1 ft., C = 7 ft., the green box weighs 30 lbs. and the blue box weighs 50 lbs., what does the orange box have to weigh for this lever to balance?

44% Answer Correctly

	30 lbs.
	31.43 lbs.
	125.71 lbs.
	10.48 lbs.

Solution

In order for this lever to balance, the torque acting on each side of the fulrum must be equal. So, the torque produced by A must equal the torque produced by B and C. Torque is weight x distance from the fulcrum which means that the following must be true for the lever to balance:

f_Ad_A = f_Bd_B + f_Cd_C

For this problem, this equation becomes:

30 lbs. x 9 ft. = 50 lbs. x 1 ft. + f_C x 7 ft.

270 ft. lbs. = 50 ft. lbs. + f_C x 7 ft.

f_C = \( \frac{270 ft. lbs. - 50 ft. lbs.}{7 ft.} \) = \( \frac{220 ft. lbs.}{7 ft.} \) = 31.43 lbs.

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

84% Answer Correctly

	inclined plane
	wedge
	first-class lever
	none of these

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.

The force required to initally get an object moving is __________ the force required to keep it moving.

76% Answer Correctly

	opposite
	the same as
	higher than
	lower than

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).