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## Homework Statement

Two divers jumped from a 3m platform. One jumps upward at 1.8ms^-1 and the second steps off the platform as the first passes it on the way down.

a) What are their speeds as they hit the water?

b) Which hits the water first and by how much?

## Homework Equations

## The Attempt at a Solution

a) What are their speeds as they hit the water?

Diver 1:

Calculate distance diver 1 travels as he jumps 1.8ms^-1 upwards off the platform.

vf^2 - vi^2 = 2g(yf - yi)

0 - (18ms^-1)^2 = 2(-9.8ms^-2)(yf - yi)

yf - yi = 0.165m

3 m + 0.165m = 3.165m

vf^2 - vi^2 = 2g(yf - yi)

vf = 7.8ms^-1

diver 1 hits water at 7.8ms^-1

Diver 2:

vf^2 - vi^2 = 2g(yf - yi)

vf^2 - 0 = 2(-9.8ms^-2)(-3m)

vf = 7.6ms^-1

Diver 2 hits water at 7.6ms^-1

b) Which hits the water first and by how much?

Diver 1:

At the instant at which diver 1 is 3.165m off the ground, vi = 0

-3.165m = 0.5(0ms^-1 + (-7.8ms^-1))t

t = 0.8s

Diver 2:

-3 = 0.5(0ms^-1 + (-7.6ms^-1))t

t = 0.78s

My answers are wrong according to the book:

a) -7.67ms^-1

b) 0.162s

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