EK Physics Q290

[silverice]

---

Members do not see this ad.

A box is rested on a scale on a elevator floor. The elevator's acceleration is 1m/s^2. The maximum velocity is 5m/s. The floors of the building are separated by 5m. The box has a mass of 10kg.

What's the maximum apparent weight of the box during a trip from the third floor to the first floor?

80N, 90N, 100N or 110N

Answer: 110N Explanation: W=mg+ma

My question is, the elevator is decelerating, shouldn't it be mg-ma? Or is it referring to the brief moment when the elevator stops it accelerates for a couple seconds or so?

 

[Laureatebarrel]

It will accelerate and decelerate. The question asks for greatest apparent weight which can only be achieved if the elevator decelerates. So apparent weight = mg + ma. You can simply eliminate A B C because greatest apparent weight means that it must have increased weight during the trip.

 

[silverice]

Got it, thx.