- #1
vmercadooo
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Homework Statement
Gwen releases a rock at rest from the top of a 40 m tower. If g = 9.8 m/s2 and air resistance is negligible, what is the speed of the rock as it hits the ground?
v0 = initial velocity = 0
a = acceleration = 9.8
Δy = displacement in y direction = -40
v = final velocity = ?
Homework Equations
v2 = v02 + 2aΔy
The Attempt at a Solution
v2 = v02 + 2aΔy
v2 = 0 + 2 (9.8) (-40)
v2 = -784
but v2 can't be a negative number. I'm guessing either delta y is not supposed to be negative, but I thought it should be since the rock is falling, not being thrown upwards, or gravity should be negative, but I thought that when motion is downwards, the acceleration due to gravity should be positive.