# Need help finding initial velocity

## Homework Statement

A football started on the ground 64 yards from the base of the goal post and barely clears the 10 ft high bar. The initial trajectory of the football was 43 deg above the horizontal. What was its initial speed?

## The Attempt at a Solution

(vf)^2 = (vi)^2 + 2a(x)
(0) = (vi)^2 + 2(-9.8)(10)

haruspex
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(vf)^2 = (vi)^2 + 2a(x)
(0) = (vi)^2 + 2(-9.8)(10)
What, precisely, does vi represent in that equation?

SteamKing
Staff Emeritus
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## Homework Statement

A football started on the ground 64 yards from the base of the goal post and barely clears the 10 ft high bar. The initial trajectory of the football was 43 deg above the horizontal. What was its initial speed?

## The Attempt at a Solution

(vf)^2 = (vi)^2 + 2a(x)
(0) = (vi)^2 + 2(-9.8)(10)
Be careful here. The height of the bar which the football clears is measured in feet. The distance the ball starts from the goal is measured in yards. You have g measured in m/s2. Pick a unit system and put everything in consistent units. BTW, 9.8 m/s2 ≈ 32.2 ft/s2