Question

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

An autonomous warehouse transport vehicle with a mass of 2,000 kg2,000 \text{ kg} experiences a constant frictional resistance of 2,000 N2,000 \text{ N} while moving across a level concrete floor. When its electric motors produce a forward thrust of 6,000 N6,000 \text{ N}, the vehicle accelerates at a steady rate. If the motors are commanded to double their forward thrust to 12,000 N12,000 \text{ N} while the frictional resistance remains unchanged, what is the vehicle's new acceleration?

  1. A
    4.0 m/s24.0 \text{ m/s}^2
  2. 5.0 m/s25.0 \text{ m/s}^2Answer
  3. C
    6.0 m/s26.0 \text{ m/s}^2
  4. D
    0.5 m/s20.5 \text{ m/s}^2

Answer

The new acceleration is 5.0 m/s25.0 \text{ m/s}^2.
According to Newton's Second Law, acceleration is determined by the net force acting on an object (a=Fnetma = \frac{F_{net}}{m}). The net force is the forward thrust minus the friction. With a new thrust of 12,000 N12,000 \text{ N} and a constant friction of 2,000 N2,000 \text{ N}, the net force is 10,000 N10,000 \text{ N}. Dividing this by the mass of 2,000 kg2,000 \text{ kg} yields an acceleration of 5.0 m/s25.0 \text{ m/s}^2.

Step-by-Step Solution

1
Identify the forces acting on the vehicle in the new scenario.
Forward thrust (FthrustF_{thrust}) = 12,000 N12,000 \text{ N}. Frictional resistance (FfrictionF_{friction}) = 2,000 N2,000 \text{ N}.
Newton's Second Law requires the net force, which is the sum of all opposing forces.
2
Calculate the new net force.
Fnet=12,000 N−2,000 N=10,000 NF_{net} = 12,000 \text{ N} - 2,000 \text{ N} = 10,000 \text{ N}.
The net force is the actual force available to accelerate the mass.
3
Apply Newton's Second Law (F=maF = ma) to find the new acceleration.
a=Fnetm=10,000 N2,000 kg=5.0 m/s2a = \frac{F_{net}}{m} = \frac{10,000 \text{ N}}{2,000 \text{ kg}} = 5.0 \text{ m/s}^2.
Acceleration is equal to the net force divided by the mass.

Key Concept

Acceleration is directly proportional to the net force, not just the applied force. To find acceleration, all opposing forces must be subtracted from the applied force before dividing by mass.
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