What was the splashdown speed?

Question

A 60 kg stuntperson runs off a cliff at 5.2 m/s and lands safely in the river 12.4 m below. What was the splashdown speed?

_____ m/s

Understanding the relationship between potential energy, kinetic energy, the conservation of energy and work

Answer 1

Ans: V(splashdown) =16.4 m/s
This is why

1. Pe=Ke (potential energy at the top (Pe) =Kinetic energy (Ke) at splashdown)
Pe=mgh
Ke=.5mV^2
m- mass
g – acceleration due to gravity
h – height
V – vertical velocity
we have
mgh=.5mV^2
V=sqrt(2gh)
V=sqrt(2 x 9.81 x 12.4)
V=15.6m/s

Or

2. h=.5gt^2 and we know that V=gt
t=sqrt(2h/g) substituting in equation fro V we have
V=sqrt(2h/g)
V=sqrt(2hg) same equation as earlier that means we are on the right track.

But V=Vv=15.6 m/s is not the answer since we also have a horizontal component Vh.
V(splashdown) = sqrt ((Vv)^2 + (Vh)^2)=
V(splashdown) = sqrt ((15.6)^2 + (5.2)^2)=
V(splashdown) =16.4 m/s