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(II) An object is hanging by a string from your rearview mirror. While you are accelerating at a constant rate from rest to 28 m/s in 5.0 s, what angle θ does the string make with the vertical? See Fig. 4–46.
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6. Intro to Forces (Dynamics)
Newton's First & Second Laws
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An elevator is going up at a constant speed in a very tall building. Assume the only forces acting on the elevator are a downward weight force and the force of a cable pulling the elevator up. Ignore air resistance and friction. How does the magnitude of the weight force compare to the magnitude of the force of the cable?
A
The force of the cable is greater than the weight.
B
The force of the cable is less than the weight.
C
There is not enough information to answer this question.
D
The force of the cable is equal to the weight.
Verified step by step guidance1
Begin by identifying the forces acting on the elevator. In this scenario, there are two forces: the downward weight force due to gravity and the upward force exerted by the cable.
Since the elevator is moving at a constant speed, according to Newton's first law, the net force acting on the elevator must be zero. This means the forces are balanced.
For the forces to be balanced, the magnitude of the upward force exerted by the cable must be equal to the magnitude of the downward weight force.
Express this relationship mathematically using Newton's second law: \( F_{cable} = F_{weight} \), where \( F_{cable} \) is the force exerted by the cable and \( F_{weight} \) is the gravitational force on the elevator.
Conclude that since the elevator is moving at a constant speed and the net force is zero, the force of the cable is equal to the weight of the elevator.
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