SIFT Physics and Simple Machines Questions and Answers — Questions and Answers
Question 1: An aircraft is in straight and level flight at a constant velocity. Which of the following statements about the four fundamental forces acting on it is true?
- Thrust is greater than drag.
- Lift is greater than weight.
- Thrust equals drag, and lift equals weight. (Correct answer)
- Lift equals drag, and thrust equals weight.
Correct answer: Thrust equals drag, and lift equals weight.
According to Newton's First Law of Motion, an object in motion will stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force. For an aircraft to maintain a constant velocity (unaccelerated, straight, and level flight), all forces must be in equilibrium. This means the forward force (thrust) must be equal to the rearward force (drag), and the upward force (lift) must be equal to the downward force (weight).
Question 2: A winch uses a handle with a rotational radius of 15 inches to turn an axle with a radius of 3 inches. What is the ideal mechanical advantage (IMA) of this wheel and axle system?
- 45
- 12
- 0.2
- 5 (Correct answer)
Correct answer: 5
The ideal mechanical advantage (IMA) of a wheel and axle is calculated by dividing the radius of the wheel by the radius of the axle. In this scenario, IMA = Radius of Wheel / Radius of Axle = 15 inches / 3 inches = 5.
Question 3: A crane lifts a 500-pound engine 8 feet into the air. If the lift takes 4 seconds to complete, what is the power expended by the crane, ignoring friction?
- 1000 ft-lbs/sec (Correct answer)
- 4000 ft-lbs/sec
- 125 ft-lbs/sec
- 16,000 ft-lbs/sec
Correct answer: 1000 ft-lbs/sec
First, calculate the work done: Work = Force × Distance = 500 lbs × 8 ft = 4000 ft-lbs. Next, calculate the power, which is the rate at which work is done: Power = Work / Time = 4000 ft-lbs / 4 seconds = 1000 ft-lbs/sec.
Question 4: In a third-class lever, which of the following is located between the other two components?
- The fulcrum
- The load (resistance)
- The effort (force) (Correct answer)
- The mechanical advantage
Correct answer: The effort (force)
The defining characteristic of a third-class lever is that the effort (applied force) is located between the fulcrum (pivot point) and the load (resistance). This arrangement results in a mechanical advantage of less than one but provides gains in speed and range of motion. Examples include tweezers, fishing rods, and the human forearm.
Question 5: Using a block and tackle pulley system with an ideal mechanical advantage (IMA) of 4, how much rope must a user pull to lift a heavy object a vertical distance of 3 feet?
- 0.75 feet
- 3 feet
- 12 feet (Correct answer)
- 7 feet
Correct answer: 12 feet
In an ideal pulley system, the amount of rope that must be pulled is the product of the ideal mechanical advantage (IMA) and the distance the load is lifted. Therefore, Rope Pulled = IMA × Distance Lifted = 4 × 3 feet = 12 feet. The user trades pulling a longer distance for applying less force.
Question 6: A screw is a simple machine that is functionally a modification of which other simple machine?
- A wheel and axle
- An inclined plane (Correct answer)
- A lever
- A pulley
Correct answer: An inclined plane
A screw is best described as an inclined plane wrapped helically around a central axis or cylinder. The threads of the screw act as the sloped surface, converting rotational force (torque) into a linear force along the axis of the screw.
SIFT Physics and Simple Machines Questions and Answers
An aircraft is in straight and level flight at a constant velocity.
Which of the following statements about the four fundamental forces acting on it is true?