- #1

MrGoATi

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## Homework Statement

sportsman jumps at 5m/s velocity from 5m cliff to water. at what speed does he reach water?

so

given answer is 11.1m/s though in this book there are some wrong answers

(I did try other equations and I got right answer but I want to know why I can't get it using this one)

##g=-10m/s^2##

##v_0=-5m/s##

##h_0=0m##

h=-5m

## Homework Equations

I'm trying to do this using ##E_k1 + E_p1 = E_k2 + E_p2##

##E_k=\frac {mv^2}{2}##

##E_p=mgh=\frac {2mgh}{2}##

## The Attempt at a Solution

since ##h_0=0## ##E_p1=0##

putting in values

##\frac {mv_0^2}{2}=\frac {mv^2}{2}+\frac {2mgh}{2}##

after multiplying everything by 2 and dividing by m

##v_0^2=v^2+2gh##

##v^2=v_0^2-2gh##

##h=h_1-h_0##

##v^2=(-5)^2-2*(-10)*(-5-0)=25-100=-75##

v=root from -75=impossible. and root from 75 is wrong answer.

if I used one positive number in -2gh part I will get right answer. I think I might need to use |h| in these kind of formulas?

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