Question

Lift A is going up with velocity 20m/s and acceleration of $8m/s^2$ in the downward direction. While lift B is going down with 10m/s and acceleration of $+2m/s^2$ in upward direction. At this moment a bolt in the ceiling of lift A gets loose and falls. Height of the lift is 16 m.Find the displacement of bolt relative to B when it hits the floor of A.

• A. 20 m
• B. 24 m
• C. 32 m
• D. 36 m

Answer 1

The correct option is B

24 m

Displacement of bolt at 4s:
$S_b=20\times 4-\frac{1}{2}10(4{)}^2=0m$

Displacement of lift B at 4s:
$S_B=10\times 4-\frac{1}{4}10(4{)}^2=24mdownward$

So displacement of bolt relative to B:
$\frac{S_b}{b}=0-24=-24m$