Question

A lift start from rest. Its acceleration is plotted against time. When it comes to rest its height above its starting point is

• A. $20m$
• B. $64m$
• C. $32m$
• D. $36m$

Answer 1

Answer: (B)

$64m$

From 0- 4 s the motion is with constant acceleration, the distance can be calculated from kinematics equation
$S_{0-4}=0+\frac{1}{2}2\times 4^2=16m$
From 4- 8 s the motion is with constant velocity $v=u+at=0+2\times 4=8m/s$
$S_{4-8}=v\times t=8\ast 4=32m$
From 8- 12 s the motion is with constant acceleration, the distance can be calculated from kinematics equation
$S_{8-12}=8\times 4-\frac{1}{2}2\times 4^2=16m$
total distance covered$=16+32+16m=64m$