WTMA Center of Gravity and Stability 5 — Questions and Answers
Question 1: A worker hangs a heavy tool bag on one handle of a wheelbarrow. Compared to placing the bag in the bucket, this makes the wheelbarrow:
- Easier to balance because weight is lower
- Harder to control because the center of gravity shifts sideways (Correct answer)
- Identical in handling since total weight is unchanged
- More stable because the wheel bears more load
Correct answer: Harder to control because the center of gravity shifts sideways
Hanging weight on one handle shifts the center of gravity to one side, creating an unbalanced lateral torque that is difficult to counter.
Question 2: A ship's ballast tanks are filled with water low in the hull during a storm. This practice:
- Raises the center of gravity, making the ship faster
- Lowers the center of gravity, increasing stability in heavy seas (Correct answer)
- Has no effect on the ship's stability
- Raises the ship higher in the water, reducing wave impact
Correct answer: Lowers the center of gravity, increasing stability in heavy seas
Filling low ballast tanks adds mass near the keel, lowering the center of gravity and improving the ship's righting moment in rough conditions.
Question 3: A solid cylinder and a hollow tube of the same outer diameter, height, and total weight are placed on an inclined surface. Which is more stable against rolling?
- The solid cylinder, because its mass is uniformly distributed
- The hollow tube, because its mass is concentrated at the outer edge increasing rotational inertia (Correct answer)
- They are equally stable since they weigh the same
- Neither will roll on an inclined surface
Correct answer: The hollow tube, because its mass is concentrated at the outer edge increasing rotational inertia
The hollow tube has more mass concentrated at the outer radius, giving it higher rotational inertia and greater resistance to changes in rotation.
Question 4: A tower crane has a long horizontal arm (jib) with a counterweight on the short end. If a very heavy load is suspended near the tip of the long end, the crane operator should:
- Extend the jib farther to gain more leverage
- Keep the load as close to the mast as possible to avoid tipping (Correct answer)
- Remove the counterweight to reduce total weight
- Raise the load quickly to clear the center of gravity issue
Correct answer: Keep the load as close to the mast as possible to avoid tipping
Keeping the load close to the mast reduces the moment arm, decreasing the tipping torque on the crane's base.
Question 5: A vending machine being moved on a dolly is tilted back to about 45 degrees. At this angle, it is:
- Very stable because it is far from vertical
- At high risk of tipping because the center of gravity is near the edge of the support base (Correct answer)
- More stable than when upright because the base is now larger
- Perfectly balanced because weight equals tipping force
Correct answer: At high risk of tipping because the center of gravity is near the edge of the support base
At 45 degrees, the center of gravity of a tall object is close to or beyond the edge of the dolly's support base, making tip-over likely.
Question 6: A mechanic uses a pry bar to move a heavy engine block. When the fulcrum (pivot) is placed closer to the engine block, the force the mechanic must apply:
- Increases because the lever arm is shorter on the effort side (Correct answer)
- Decreases because the load is closer to the pivot
- Stays the same regardless of fulcrum position
- Increases because the engine is too heavy to leverage
Correct answer: Increases because the lever arm is shorter on the effort side
Moving the fulcrum closer to the load shortens the load arm but also shortens the effort arm even more, requiring greater force from the mechanic.
Question 7: A race car is built with a very low body and a wide wheel track to improve stability. The primary reason this design works is:
- It reduces air resistance, which lowers center of gravity
- It lowers the center of gravity and widens the support base simultaneously (Correct answer)
- Wide tires have lower rolling resistance
- A low body reduces driver visibility, improving focus
Correct answer: It lowers the center of gravity and widens the support base simultaneously
A low body places the center of gravity close to the ground, and a wide wheel track widens the support base, both of which greatly increase resistance to tipping.
WTMA Center of Gravity and Stability 5
A worker hangs a heavy tool bag on one handle of a wheelbarrow.
Compared to placing the bag in the bucket, this makes the wheelbarrow: