(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

What did I do wrong? My book's answer says the initial velocity when the rock was thrown straight down off a cliff was vi= 15.2m/s, but I got vi= -15.2m/s.

What is the initial speed of stone 2?

yi= 50m

yf= 0m

ti= 0s

tf=2.0s

ay= -9.8m/s^2

Vyf= 0m/s

Vyi= Unknown

2. Relevant equations

yf= yi + vi (change in time) + 1/2 (ay) (change in time)^2

1.)Subtract yi from both sides gives:

yf - yi = vi (change in time) + 1/2 (ay) (change in time)^2

2. Subtract (1/2 (ay) (change in time)^2) from both sides gives:

yf - yi - (1/2 (ay) (change in time)^2) = vi (change in time)

3. Divide both sides by (change in time) gives:

(yf - yi - (1/2 (ay) (change in time)^2)) / (change in time) = vi

3. The attempt at a solution

(yf - yi - (1/2 (ay) (change in time)^2)) / (change in time) = vi

(0m - 50m - (1/2 (-9.8m/s^2) (2.0s)^2)) / (2.0 s) = vi

= -15.2m/s

My textbook says vi= 15.2 m/s

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# Homework Help: Negative Ans, What is wrong?

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