projectile motion- help needed please!!! (1 Viewer)

NizDiz · Jun 3, 2013

Hey guys, if anyone can help me to approach this question and get answer, would be greatly appreciated!

A ball is projected horizontally from a cliff of height 245m, and reaches the ground at a horizontal difference of 350m from the foot of the tower. Determine the initial velocity V, and the velocity (direction and magnitude) on striking the ground (g = 10m/s^2)

(Answer is V=50m/s, 10(74)^1/2 at an angle of 125 degrees 32 minutes)

jmk123 · Jun 3, 2013

NizDiz said:
Hey guys, if anyone can help me to approach this question and get answer, would be greatly appreciated!

A ball is projected horizontally from a cliff of height 245m, and reaches the ground at a horizontal difference of 350m from the foot of the tower. Determine the initial velocity V, and the velocity (direction and magnitude) on striking the ground (g = 10m/s^2)

(Answer is V=50m/s, 10(74)^1/2 at an angle of 125 degrees 32 minutes)

If projected horizontally, angle of projection=0.

Write out ur equations with that in mind, answer will come much easier.

HeroicPandas · Jun 3, 2013

Drongoski said:
$\" x \D x$

Want to post solution - but forgot how to specify x-dot, x-double dot etc. Help anyone.

{\dot{x}} x -dot
{\ddot{x}} x-double dot

Drongoski · Jun 3, 2013

Thanks - I just found that out too; last time I used it was over a year ago.

Drongoski · Jun 3, 2013

$\dot x(0) = V $ and $ \dot y(0) = 0$

$\ddot x = 0 \implies \dot x = \int 0 dt = C$

$\therefore C = V \implies \dot x (t) = V$

$\therefore x = \int V dt = Vt + D$

$x(0) = 0+D = 0 \implies x(t) = Vt$

$\ddot y = -10 \implies \dot y = \int -10 dt = -10t + E$

$\dot y(0) = 0+E = 0 \implies \dot y(t) = -10t$

$\therefore y = \int -10t dt = -5t^2 + F$

$y(0) = 0+F = 0 \implies y(t) = -5t^2$

Say ball hits ground when t = T

$\therefore -5T^2 = -245 \implies T^2 = 49 \implies T = 7$

$\therefore VT = 350 \implies V = 50$

$$now $ \dot y(7) = -10 \times 7 = -70 $ and $ \dot x(7) = V = 50$

$\therefore $angle of inclination $ \theta = tan ^{-1}(\frac { -70}{50}) = 180 ^\circ - 54 ^\circ 28 '$

How do you specify the bloody degree symbol??

Fixed - thanks Carrot.

Carrotsticks · Jun 3, 2013

^\circ

Drongoski · Jun 3, 2013

ah - thanks for coming to the rescue, Carrot.

projectile motion- help needed please!!! (1 Viewer)

NizDiz

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jmk123

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HeroicPandas

Heroic!

Drongoski

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Carrotsticks

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Drongoski

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