WTMA Center of Gravity and Stability 3 — Questions and Answers
Question 1: A rectangular block is tipped until it balances on its corner. At that tipping point, the center of gravity is located:
- Below the pivot corner
- Directly above the pivot corner (Correct answer)
- At the geometric center of the block
- At the midpoint of the base
Correct answer: Directly above the pivot corner
An object is at the tipping point when its center of gravity is directly over the pivot point — any further tipping causes it to fall.
Question 2: A shelf bracket is rated to hold 50 lbs when the load is placed 6 inches from the wall. If the same 50 lb load is placed 12 inches from the wall, the bracket experiences:
- Half the stress because the load is spread over more distance
- Twice the stress because the moment arm doubled (Correct answer)
- The same stress since load weight didn't change
- Reduced stress because the shelf now flexes
Correct answer: Twice the stress because the moment arm doubled
Torque equals force times distance; doubling the distance from the pivot (wall) doubles the bending moment on the bracket.
Question 3: A motorcycle is more stable against tipping side-to-side when traveling at speed primarily because of:
- The narrow tire width keeping the center of gravity low
- Gyroscopic effect from the spinning wheels resisting lean (Correct answer)
- The engine weight being close to the ground
- The handlebar width providing a wide grip base
Correct answer: Gyroscopic effect from the spinning wheels resisting lean
Spinning wheels create gyroscopic stability that resists changes in the lean angle, helping keep the motorcycle upright.
Question 4: A crane lifts a load on a long boom extended horizontally. As the boom extends farther out, the crane's overall center of gravity:
- Moves toward the counterweight side
- Moves toward the load side (Correct answer)
- Stays at the same point regardless of boom extension
- Drops lower to the ground
Correct answer: Moves toward the load side
Extending the boom moves the suspended load farther from the crane's base, shifting the combined center of gravity toward the load side.
Question 5: An empty oil drum standing upright has its center of gravity approximately:
- At the very bottom
- At the midpoint of its height (Correct answer)
- At the very top
- At the rim of the drum
Correct answer: At the midpoint of its height
A uniform hollow cylinder has its center of gravity at the geometric center, which is at the midpoint of its height.
Question 6: A worker pushes a heavy cart up a ramp. The cart is most likely to tip backward when:
- The ramp is flat and long
- The ramp is steep and the load is high on the cart (Correct answer)
- The cart has large wheels
- The worker pushes from the side
Correct answer: The ramp is steep and the load is high on the cart
A steep ramp combined with a high center of gravity shifts weight toward the rear of the cart relative to its base, promoting backward tipping.
Question 7: Which shape has the lowest center of gravity relative to its height?
- A tall thin cylinder
- A wide flat cone with the base at the bottom (Correct answer)
- A cube balanced on one corner
- A sphere resting on a flat surface
Correct answer: A wide flat cone with the base at the bottom
A wide flat cone with its base down has most of its mass concentrated near the base, placing the center of gravity very low.
WTMA Center of Gravity and Stability 3
A rectangular block is tipped until it balances on its corner.
At that tipping point, the center of gravity is located: