Question

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

An industrial robotic actuator pushes a 2,000 kg2,000 \text{ kg} steel casting along a horizontal assembly rail. The actuator applies a continuous forward force of 5,000 N5,000 \text{ N}, while friction from the rail creates an opposing force of 1,000 N1,000 \text{ N}. What is the forward acceleration of the steel casting?

  1. A
    0.5 m/s20.5 \text{ m/s}^2
  2. 2.0 m/s22.0 \text{ m/s}^2Answer
  3. C
    2.5 m/s22.5 \text{ m/s}^2
  4. D
    20.0 m/s220.0 \text{ m/s}^2

Answer

The correct forward acceleration is 2.0 m/s22.0 \text{ m/s}^2.
The correct answer is found by first determining the net force acting on the casting. Subtract the 1,000 N1,000 \text{ N} opposing friction from the 5,000 N5,000 \text{ N} applied force to get a net force of 4,000 N4,000 \text{ N}. Then, apply Newton's Second Law (a=F/ma = F/m) by dividing the 4,000 N4,000 \text{ N} net force by the 2,000 kg2,000 \text{ kg} mass, resulting in 2.0 m/s22.0 \text{ m/s}^2.

Step-by-Step Solution

1
Determine the net force acting on the steel casting.
Fnet=5,000 N (applied)−1,000 N (friction)=4,000 NF_{\text{net}} = 5,000 \text{ N} \text{ (applied)} - 1,000 \text{ N} \text{ (friction)} = 4,000 \text{ N}
When multiple forces act on an object, you must find the overall net force before calculating acceleration. Opposing forces are subtracted.
2
Use Newton's Second Law (F=maF = ma) to solve for acceleration (a=F/ma = F/m).
a=4,000 N2,000 kg=2.0 m/s2a = \frac{4,000 \text{ N}}{2,000 \text{ kg}} = 2.0 \text{ m/s}^2
Acceleration is directly proportional to the net force and inversely proportional to the mass.

Key Concept

Newton's Second Law and Net Force Calculation
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