Question

The elevation at ground level is 0 feet. An elevator starts 90 feet below ground level. After traveling for 15 seconds, the elevator is 20 feet below ground level. Which statement describes the elevators rate of change during this 15 second interval?

A. The elevator traveled upward at a rate of 6 ft per second
B. The elevator traveled upward at a rate of 4 2/3 feet per second.
C. The elevator traveled downward at a rate of 6ft per second.
D. The elevator traveled downward at a rate of 4 2/3 feet per second

Answer 1

Its D, 90-20=70 ft traveled downwards.

Answer 2

The answer is option (B) i.e. The elevator traveled upward at a rate of
`4 (2)/(3)` ft/sec.

So, we say at time, t = 0, the elevator just starts moving upwards and at time t = 0, the elevator is 90 ft below the ground.

Now, after 15 seconds, the elevator is 20 ft below the ground.
It means, the elevator has covered a distance of 90-20=70 ft in time 15 seconds.
So, speed of elevator moving upwards is:


`(70 ft)/(15 sec)` =
`4 (2)/(3)`ft/sec