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 COI N 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 1S . CALCULATE FROM THESE DATA THE ACCELERATION OF THE ELEVATOR .

Answer 1

Solution:

For elevator and coin : Initial velocity=u=0m/s

As the elevator descends  with uniform acceleration "a" the coin has to move more distance than 1.8cm to strike floor.

time taken =t=1 sec

Scoin=Sc=ut+1/2at²

Sc= 0+1/2at²

=1/2 xg x1²

Sc=g/2

Se=ut+1/2 at²

=0+1/2 a(1)²

Se=a/2

Total distance travelled by coin is given by :

1.8 +1/2 a =1/2g

1.8 +a/2 =g/2

1.8+a/2=9.8/2

a/2=4.9 -1.8=3.1m

a=6.2 m/s2

a= 6.2 x 3.28 = 20.34 ft/s²