Question

Difficulty: MediumNewton's Second Law (F=ma)

A military hovercraft with a mass of 6,000 kg6,000 \text{ kg} is transporting equipment across a frozen lake. The hovercraft's thrusters generate a forward force of 27,000 N27,000 \text{ N}, while air resistance and surface friction create a combined opposing force of 9,000 N9,000 \text{ N}. What is the forward acceleration of the hovercraft?

  1. 3.0 m/s23.0 \text{ m/s}^2Answer
  2. B
    4.5 m/s24.5 \text{ m/s}^2
  3. C
    0.3 m/s20.3 \text{ m/s}^2
  4. D
    0.33 m/s20.33 \text{ m/s}^2

Answer

The correct forward acceleration of the hovercraft is 3.0 m/s23.0 \text{ m/s}^2.
The correct answer accurately determines the net force by subtracting the opposing friction (9,000 N9,000 \text{ N}) from the applied thrust (27,000 N27,000 \text{ N}) to get 18,000 N18,000 \text{ N}. Dividing this net force by the mass (6,000 kg6,000 \text{ kg}) yields an acceleration of 3.0 m/s23.0 \text{ m/s}^2.

Step-by-Step Solution

1
Calculate the net forward force acting on the hovercraft.
Fnet=27,000 N−9,000 N=18,000 NF_{net} = 27,000 \text{ N} - 9,000 \text{ N} = 18,000 \text{ N}
Acceleration is determined by the net force, which is the sum of all forces acting on the object. The opposing force must be subtracted from the forward thrust.
2
Set up Newton's Second Law equation.
Fnet=m×aF_{net} = m \times a
This formula relates net force, mass, and acceleration.
3
Rearrange the equation to solve for acceleration and substitute the known values.
a=18,000 N6,000 kg=3.0 m/s2a = \frac{18,000 \text{ N}}{6,000 \text{ kg}} = 3.0 \text{ m/s}^2
Dividing the net force by the mass gives the resulting acceleration.

Key Concept

Newton's Second Law states that the acceleration of an object is directly proportional to the net force acting upon it and inversely proportional to its mass (a=Fnetma = \frac{F_{net}}{m}).
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