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March 29, 2015

March 29, 2015

Posted by **Elisa** on Sunday, June 1, 2008 at 12:43pm.

How long after being released does the stone strike the beach below the cliff?

I got 3.67 s.

With what speed and angle of impact does the stone land?

I got 38.97 m/s for the speed, but I cannot figure out the angle. It says that the answer is in degrees "below the horizontal."

I calculated x to be 55.23m and I tried to calculate -y, but I keep getting the wrong angle. After getting -y I though I was supposed to do arctan(opp/adj) to get the angle "below the horizontal."

Please help! Thanks!

- Physics -
**drwls**, Sunday, June 1, 2008 at 12:56pmT = 3.67 s is correct for the time to impact. When thowing horizontally, the speed does not affect the time to hot the ground.

Using conservation of energy for the speed Vf at impact,

(1/2) Vf^2 = Vo^2/2 + g H

(1/2) Vf^2 = (15^2)/2 + 9.8*66

= 759.3 m^2/s^2

Vf = 38.97 m/s

The tangent of the angle at impact, measured below the horizontal, is Vy/Vx at impact

theta = arctan (g*T)/15 m/s

= arctan 35.97/15 = 67.4 degrees

- Physics -
**Elisa**, Sunday, June 1, 2008 at 1:18pmThanks!

- Physics -
**drwls**, Monday, June 2, 2008 at 1:38amIt is also arcsin g*T/38.97, where 38.97 is the speed. This gives you the same angle.

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