AFCT Mechanical Aptitude 2 — Questions and Answers

Question 1: A wheelbarrow is an example of which class of lever?

First class
Second class (Correct answer)
Third class
It is not a lever

Correct answer: Second class

A wheelbarrow is a second-class lever: fulcrum (wheel) at one end, effort (handles) at the other, load between them.

In a second-class lever, the load is between fulcrum and effort. Wheelbarrow: wheel = fulcrum, heavy load in tray = between, handles = effort. This always gives mechanical advantage greater than 1. Other examples: nutcracker, bottle opener.

Question 2: If a 20-tooth gear drives a 60-tooth gear, what is the gear ratio?

1:3 (Correct answer)
3:1
1:2
2:1

Correct answer: 1:3

Gear ratio = driving gear teeth : driven gear teeth = 20:60 = 1:3.

The gear ratio compares driving to driven: 20:60 = 1:3. For every 1 revolution of the driving gear, the driven gear turns 1/3 revolution. The driven gear rotates slower but with 3 times the torque.

Question 3: Which statement about friction is correct?

Friction always acts in the direction of motion
Static friction is generally greater than kinetic friction (Correct answer)
Friction is independent of surface contact area
Smoother surfaces always have zero friction

Correct answer: Static friction is generally greater than kinetic friction

Static friction (resistance to starting motion) is typically greater than kinetic friction (resistance during motion).

Static friction is generally greater than kinetic friction. It takes more force to start moving a heavy box than to keep it sliding. Friction opposes motion direction. While approximately independent of contact area for rigid surfaces, smoother surfaces reduce but never eliminate friction.

Question 4: A spring scale reads 10 pounds when a box is hung from it. Pulled horizontally on a table, the scale reads 4 pounds to start sliding. What is the coefficient of static friction?

0.25
0.4 (Correct answer)
2.5
0.6

Correct answer: 0.4

Coefficient of static friction = friction force / normal force = 4 / 10 = 0.4.

Coefficient of static friction = friction force / normal force. On a flat surface, normal force equals weight: 10 pounds. Friction force = 4 pounds. So coefficient = 4/10 = 0.4, meaning friction is 40% of normal force.

Question 5: What happens to mechanical advantage as an inclined plane's angle decreases (becomes more gradual)?

It decreases
It increases (Correct answer)
It stays the same
It becomes zero

Correct answer: It increases

A more gradual inclined plane has greater mechanical advantage: less force needed but longer distance.

Mechanical advantage of an inclined plane is length/height. As the angle decreases, the plane gets longer relative to height, increasing MA. A gentle slope needs little force but a long push. This is why mountain roads use switchbacks.

Question 6: A ball is thrown straight up into the air. At the highest point of its trajectory, what is its velocity?

Maximum
Zero (Correct answer)
Equal to its initial velocity
Negative

Correct answer: Zero

At the highest point, the ball momentarily stops before falling back down, so its velocity is zero.

At the apex, the ball has decelerated to zero velocity before gravity accelerates it downward. However, acceleration due to gravity is NOT zero at this point; it remains constant throughout the flight. The ball changes direction because constant downward force eventually reverses its upward velocity.

AFCT Mechanical Aptitude 2

A wheelbarrow is an example of which class of lever?