SIFT Physics and Simple Machines Questions and Answers 2 — Questions and Answers

Question 1: An object is accelerating at 3 m/s². If the net force on it is 15 N, what is its mass?

0.2 kg
5 kg (Correct answer)
18 kg
45 kg

Correct answer: 5 kg

Using Newton's Second Law: F = ma, so m = F/a = 15/3 = 5 kg.

Newton's Second Law (F = ma) is fundamental to mechanics. Given force in Newtons and acceleration in m/s², mass is in kilograms. Here, 15 N = m × 3 m/s², giving m = 5 kg. This law governs everything from artillery trajectory calculations to helicopter rotor thrust requirements.

Question 2: What is the unit of power in the SI system?

Joule
Newton
Watt (Correct answer)
Pascal

Correct answer: Watt

The watt (W) is the SI unit of power, equal to one joule per second (J/s). Power measures the rate at which work is done or energy is transferred.

Power = Work / Time = Energy / Time. One watt equals one joule of work done per second. In mechanical systems, power = Force × velocity. In aviation, engine power is often expressed in horsepower (1 hp = 746 W). Understanding power helps determine how quickly a system can do work.

Question 3: An object at the top of a 50-meter cliff has potential energy of 4,900 J. What is its mass? (g = 9.8 m/s²)

2 kg
5 kg
10 kg (Correct answer)
100 kg

Correct answer: 10 kg

PE = mgh, so m = PE/(gh) = 4,900/(9.8 × 50) = 4,900/490 = 10 kg.

Gravitational potential energy (PE = mgh) depends on mass, gravitational acceleration, and height. This energy converts to kinetic energy as the object falls. At the bottom, KE = ½mv² = PE (ignoring air resistance). In aviation, altitude represents stored potential energy that can be traded for airspeed.

Question 4: What is the mechanical advantage of a screw with a pitch of 0.5 cm and a handle radius of 10 cm? (MA = 2πr/p)

5
20
~125.7 (Correct answer)
0.05

Correct answer: ~125.7

MA = 2πr/p = 2π(10)/0.5 = 20π/0.5 = 40π ≈ 125.7. The screw provides tremendous mechanical advantage by converting rotation into linear force.

Screws convert rotational motion into linear force. The handle traces a large circle (circumference = 2πr) to advance the screw one pitch. MA = circumference/pitch = 2π(10)/0.5 ≈ 125.7. This is why screws can exert enormous clamping forces with minimal hand effort.

Question 5: Two identical springs, each with spring constant k=100 N/m, are connected in parallel. What is the combined spring constant?

50 N/m
100 N/m
200 N/m (Correct answer)
10,000 N/m

Correct answer: 200 N/m

Springs in parallel have their constants added: k_total = k₁ + k₂ = 100 + 100 = 200 N/m. They share the load, making the system stiffer.

In parallel, both springs stretch by the same amount, but together they support more weight. k_parallel = k₁ + k₂ + ... In series, k_series = 1/(1/k₁ + 1/k₂), which gives a softer result. Landing gear strut springs and vehicle suspension use parallel arrangements to handle heavy loads.

Question 6: What is the velocity ratio of a block-and-tackle system with 4 rope segments supporting the load?

1
2
4 (Correct answer)
8

Correct answer: 4

The velocity ratio equals the number of rope segments supporting the movable pulley. With 4 segments, for every 4 feet of rope pulled, the load rises only 1 foot.

Velocity ratio (VR) in a pulley system = number of rope sections supporting the load block. If VR=4, the operator pulls 4 feet of rope to lift the load 1 foot. The mechanical advantage equals VR (ignoring friction), meaning input force is 1/4 of the load. This trades distance for force.

SIFT Physics and Simple Machines Questions and Answers 2

An object is accelerating at 3 m/s².
If the net force on it is 15 N, what is its mass?