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May 4, 2016

# Homework Help: Physics

Posted by Tammy on Tuesday, September 25, 2007 at 6:48pm.

A projectile is shot horizontally at 30m/s from the roof of a building 100m tall. Use g=10m/s^2. Choose + vertical direction to be pwards.
a) determine the time necessary fot the projectile to reach the ground below
b) determine the horizontal distance from the base of teh building that the projectile lands
c) determine the horizontal and vertical components of the velocity just before the projectile hits the ground
d) determine the magnitude of the total velocity just before the projectile hits the ground.

a)would I use y=y_0 +v_0t +1/2 at^2
100=0+30t+1/2(10)t^2 and solve for t?
b) would i use x=x_0+v_xt
c)for the horizontal componet i believe i use v=v_0 +at and for the vertical: x=x_0+vt
d) v_total =sqrt(vx^2 +vy^2)

Are these equations I came up with correct to solve this problem?
• Physics - drwls, Tuesday, September 25, 2007 at 7:17pm

a) No. Write an equation for the vertical direction only. The vertical component of the initial velocity is zero.
y = 100 - (g/2)t^2
Set y = 0 ands solve for t.

b)The initial value of x is zero and the horizontal component of velocity remains 30 m/s. Gravity has no hoorizontal component
c) No. X = Xo + Vt will not tell you the horizontal componsnt of velocity. After solving a) for t, calculate Vy = -gt. Vx remains the initial value
x = 30
d) yes, your method is correct

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