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Question
a student, who weighs 600n, is standing on a bathroom scale and riding an elevator that is moving downwards with a speed that is decreasing at a rate of 2.8m/s². how many forces are acting on the student? what is the students mass? what is the net force on the student? which force does the scale read? what value does the scale read? (in newtons)
Sub - question 1: How many forces are acting on the student?
When a student is in an elevator, the forces acting on the student are gravity (acting downwards) and the normal force from the scale (acting upwards). So there are 2 forces.
Step1: Recall the formula for weight
The weight \( W\) of an object is given by \( W = mg\), where \( g = 9.8\ m/s^{2}\) (acceleration due to gravity) and \( m\) is the mass. We know \( W=600\ N\).
Step2: Solve for mass \( m\)
Rearranging the formula \( m=\frac{W}{g}\). Substituting \( W = 600\ N\) and \( g=9.8\ m/s^{2}\), we get \( m=\frac{600}{9.8}\approx61.22\ kg\).
Step1: Determine the acceleration
The elevator is moving downwards with a decreasing speed, so the acceleration \( a\) is upwards. The magnitude of acceleration \( a = 2.8\ m/s^{2}\).
Step2: Use Newton's second law \( F_{net}=ma\)
We know \( m\approx61.22\ kg\) and \( a = 2.8\ m/s^{2}\). So \( F_{net}=61.22\ kg\times2.8\ m/s^{2}\approx171.42\ N\). Since the acceleration is upwards, the net force is upwards.
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