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 $6 \mathrm{ft}$ 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 these data the acceleration of the elevator.
For coin-lift
$u_{\text {rel }}=0 \mathrm{~m} / \mathrm{s}$
$t_{\text {rel }}=1 \mathrm{sec}$
$\mathrm{S}_{\mathrm{rel}}=6 \mathrm{ft}$
Srel $=u_{\text {rel }} t+\frac{1}{2} a_{\text {rel }} t^{2}$
$\stackrel{1}{6}$
${ }^{2} a_{\text {rel }}(1)^{2}$
$a_{\text {rel }}=12 \mathrm{ft} / \mathrm{sec}^{2}$
$\mathrm{~g}-\mathrm{a}_{\text {lift }}=12$
$\mathrm{a}_{\text {lift }}=32-12$
$\mathrm{a}_{\text {lift }}=20 \mathrm{ft} / \mathrm{sec}^{2}$