AFCT Mechanical Comprehension 3

Question 1

An object weighing 50 pounds is on a frictionless inclined plane at 30 degrees. What force parallel to the plane keeps it stationary?

Accepted Answer

25 pounds

Answer

The force parallel to the plane equals weight times sine of the angle: 50 x sin(30) = 50 x 0.5 = 25 pounds.

Question 2

What is the mechanical advantage of a wheel and axle if the wheel radius is 12 inches and the axle radius is 3 inches?

Accepted Answer

4

Answer

Mechanical advantage = wheel radius / axle radius = 12 / 3 = 4.

Question 3

According to Newton's Third Law, when a rifle is fired, the recoil felt by the shooter is due to:

Accepted Answer

An equal and opposite reaction force

Answer

Newton's Third Law states every action has an equal and opposite reaction. The bullet going forward causes an equal force pushing the rifle backward.

Question 4

A block and tackle pulley system has 4 supporting ropes. If the load weighs 200 pounds, what effort is theoretically required?

Accepted Answer

50 pounds

Answer

Mechanical advantage equals the number of supporting ropes. With 4 ropes: 200 / 4 = 50 pounds of effort.

Question 5

Why does a wider base make an object more stable?

Accepted Answer

It keeps the center of gravity over the base more easily

Answer

A wider base means the center of gravity can shift more before falling outside the base, making it harder to tip over.

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