Your mass is 50 kg. Suppose you are standing on a scale in an elevator that is approaching a top floor and decreasing its speed at the rate of 3 m/s every second. What would be the reading on the scale?
A) 740 N
B) 640 N
C) 340 N
D) 150 N
E) 0 N

Question

Quizplus · Accepted Answer

The force that the scale measures is equal to the net force (which is the weight minus the force needed to decelerate the elevator). The weight is simply the product of the mass and the acceleration due to gravity (9.8 m/s^2). At the top floor, the elevator is not moving, so the force measured by the scale is simply the weight, which is (50 kg)(9.8 m/s^2) = 490 N. As the elevator decelerates, the force needed to slow it down increases. At a rate of 3 m/s^2, the elevator will be reducing its speed by 3 m/s every second, so the force needed to decelerate will be (50 kg)(3 m/s^2) = 150 N. Therefore, the force measured by the scale will be 490 N - 150 N = 340 N. So, the correct answer is C.

Your Mass Is 50 Kg