Physics help?

Question

A pole vaulter leaves the ground to travel 4.0 m up and over the bar, and then another 4.0 m back to the ground. It takes 1.81 s for the whole trip. Calculate the velocity with which she left the ground?

Answer 1

so it takes 0.905 s up and the same down.

v = gt = 9.8 x 0.905 = 8.87 m/s

check

h = ½gt² = ½9.8•0.905² = 3.77 m

which is NOT 4 m, so something is off....

if we use the 4 m number

v = √(2gh) = √(2•9.8•4) = 8.85 m/s

take you pick.

falling object starting from rest

h is height in meters, t is time falling in seconds,

g is acceleration of gravity, usually 9.8 m/s²

v is velocity in m/s

h = ½gt²

t = √(2h/g)

v = √(2gh)

h = v²/2g

v = gt