ASVAB Mechanical Comprehension Practice Test 689778 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.99
Score	0%	60%

Review

1 If the handles of a wheelbarrow are 2.0 ft. from the wheel axle, how many pounds of force must you exert to lift the handles if it's carrying a 240 lbs. load concentrated at a point 1.0 ft. from the axle?

52% Answer Correctly

	69
	240
	120
	-70.6

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:
\( F_e = \frac{F_r d_r}{d_e} \)
\( F_e = \frac{240 \times 1.0}{2.0} \)
\( F_e = \frac{240.0}{2.0} \)
\( F_e = 120 \)

2 If the force applied at the blue arrow over 4 ft. moves the green box 0.5 ft., what is the mechanical advantage of this lever?

56% Answer Correctly

	8.8
	8
	12
	2

Solution

Mechanical advantage (MA) can be calculated knowing only the distance the effort (blue arrow) moves and the distance the resistance (green box) moves. The equation is:

MA = \( \frac{E_d}{R_d} \)

where E_d is the effort distance and R_d is the resistance distance. For this problem, the equation becomes:

MA = \( \frac{4 ft.}{0.5 ft.} \) = 8

You might be wondering how having an effort distance of 8 times the resistance distance is an advantage. Remember the principle of moments. For a lever in equilibrium the effort torque equals the resistance torque. Because torque is force x distance, if the effort distance is 8 times the resistance distance, the effort force must be \( \frac{1}{8} \) the resistance force. You're trading moving 8 times the distance for only having to use \( \frac{1}{8} \) the force.

The work done by the sum of all forces acting on a particle equals the change in the kinetic energy of the particle. This defines which of the following?

60% Answer Correctly

	Pascal's law
	work-energy theorem
	mechanical advantage
	conservation of mechanical energy

Solution

The work-energy theorem states that the work done by the sum of all forces acting on a particle equals the change in the kinetic energy of the particle. Simply put, work imparts kinetic energy to the matter upon which the work is being done.

The mechanical advantage of a block and tackle is equal to which of the following?

69% Answer Correctly

	the number of input forces
	the number of pulleys
	the number of connecting ropes
	the number of loads

Solution

Two or more pulleys used together constitute a block and tackle which, unlike a fixed pulley, does impart mechanical advantage as a function of the number of pulleys that make up the arrangement. So, for example, a block and tackle with three pulleys would have a mechanical advantage of three.

Coplanar forces:

62% Answer Correctly

	act along the same line of action
	have opposite dimensions
	pass through a common point
	act in a common plane

Solution

Collinear forces act along the same line of action, concurrent forces pass through a common point and coplanar forces act in a common plane.