- #1

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- 0

## Homework Statement

If a car rolls gently (v0 = 0) off a vertical cliff, how long does it take it to reach 73 km/h?

A helicopter is ascending vertically with a speed of 7.50 m/s. At a height of 110 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package's initial speed equals the helicopter's.]

## Homework Equations

Vf = Vi + at

Vf^2 = Vi^2 + 2ad

d = Vi(t) + (.5)(a)(t)^2

t= Vf/a or Vf-Vi/a

## The Attempt at a Solution

For the first one : I set Vi at 0, Vf at 73, and a(acceleration) at 9.8. From there i did 73/9.8 to find the time when it is traveling 73 km/h, and got 7.44, which is obviously wrong. I'm guessing I have to find distance, but I'm not sure how.

For the second one: I set Vi at 7.5, d (distance) at 110, and a at 9.8. Then I used the Vf^2 formula to find Vf, which was 47. Then i did (47-7.5)/9.8 to get about 4 seconds, which was wrong.