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Difficulty: MediumNewton's First Law (Inertia)

A 500 kg500\text{ kg} steel pipe is suspended by a vertical cable from a motorized overhead bridge crane. The crane carriage and the suspended pipe are traveling horizontally along a straight track at a constant speed of 2 m/s2\text{ m/s}. If the crane operator suddenly engages the emergency brakes and the crane carriage stops instantly, what will initially happen to the suspended steel pipe?

  1. It will continue moving forward, swinging in the original direction of travel, due to its inertia.Answer
  2. B
    It will swing backward in the opposite direction of travel as a reaction to the crane's braking force.
  3. C
    It will stop moving horizontally, but its downward weight will momentarily increase.
  4. D
    It will stop immediately with the crane because its large mass causes it to naturally decelerate faster.

Answer

The pipe will continue moving forward, swinging in the original direction of travel, due to its inertia.
According to Newton's First Law, an object in motion will stay in motion at a constant velocity unless acted upon by an external net force. The emergency brakes apply a stopping force to the crane carriage on the track, but not directly to the suspended pipe hanging below. Therefore, the pipe's mass strongly resists the change in velocity (inertia), causing it to continue moving forward and swing in its original direction of travel.

Step-by-Step Solution

1
Identify the state of motion before the brakes are applied.
Both the crane carriage and the suspended pipe are moving horizontally at a steady speed of 2 m/s.
Establishing the initial conditions is necessary to properly apply Newton's First Law.
2
Determine where the stopping force is applied when the emergency brakes are engaged.
The braking force is applied directly to the crane carriage on the track, causing the carriage to stop abruptly.
To predict the motion of the suspended pipe, we must identify if an external horizontal force acts directly on it.
3
Apply Newton's First Law of Motion (Inertia) to the suspended pipe.
Because no direct horizontal stopping force is applied to the pipe, its inertia causes it to resist the change in motion and it attempts to continue moving forward at 2 m/s.
Newton's First Law states that an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
4
Evaluate the resulting physical behavior of the pipe.
Since the crane carriage stops but the pipe continues forward, the flexible cable allows the pipe's continued momentum to manifest as a forward swing, like a pendulum.
Visualizing the mechanical connection explains the exact physical outcome resulting from the object's inertia.

Key Concept

Newton's First Law (Inertia)
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Topics

Newton's First Law (Inertia)

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