Motion/Time Question


by Cman1494
Tags: calculus, kinematics, motion, time
Cman1494
Cman1494 is offline
#1
Sep12-11, 05:22 PM
P: 1
A hotel elevator ascends 230 m with a maximum speed of 5.8 m/s. Its acceleration and deceleration both have a magnitude of 1.0 m/s2.

(a) How far does the elevator move while accelerating to full speed from rest?
I got this part:

x = v/2a = 5.8/2(1) = 5.82/2 = 16.82 m

(b) How long does it take to make the complete trip from bottom to top?


I broke the problem up into three sections: the elevator going up (1.0 m/s2), the elevator at rest (0), and the elevator coming back down (-1.0 m/s 2). I know that the elevator goes 230 m up and then 230 m down, but I cannot figure out which kinematic equation to use or if I need to use calculus (I have limited calculus knowledge).
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lewando
lewando is offline
#2
Sep12-11, 08:41 PM
PF Gold
P: 1,054
Think about how an elevator operates as it goes up: it accelerates, travels at constant speed for a while, then decelerates. Same 3 phases on the down trip. Don't worry about the elevator at rest part--assume it goes up, stops for less than an instant, then goes back down.


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