Question

An elevator is descending with uniform acceleration. To measure the acceleration, a person in the elevator drops a coin at the moment the elevator starts. The coin is 6 ft above the floor of the elevator at the time it is dropped. The person observes that the coin strikes the floor in 1 second. Calculate from acceleration of the elevator.

• A. $20ft/s^2$
• B. $30ft/s^2$
• C. $200ft/s^2$
• D. $50ft/s^2$

Answer 1

The correct option is A $20ft/s^2$

Let the acceleration of life be a

$\Rightarrow$ acc. of ball w.r.t gourd - acc of life

$\Rightarrow$ ar

$a_{ball\left(lift\right)}=g-a$

$=9.8m/s^2-a=32ft/s-a$

displacement = $s=6ft$

$t=ls$

$u=0$

$s=ut+\frac{1}{2}a{t}^2$

$=0\ast 1+\frac{1}{2}(32-a)\times 1\times 1=\frac{1}{2}(32-a)$

$\to 6=\frac{1}{2}(32-a)$

$a=20ft/s^2$