1. ## projective fired

a projectile is fired from a cliff 100m high with a velocity of 200m/s. If the angle of projection is 20degrees above the horizontal, find the time of flight correct to 2 decimal places and the range of the projectile from the base of the cliff to the nearest metre. (assume g=9.8 metres per second per second)

Can someone please give me the answers to this question. Explanation is not nessecary. i just need to verify my answers. thanx

2. Originally Posted by chrisgo
a projectile is fired from a cliff 100m high with a velocity of 200m/s. If the angle of projection is 20degrees above the horizontal, find the time of flight correct to 2 decimal places and the range of the projectile from the base of the cliff to the nearest metre. (assume g=9.8 metres per second per second)

Can someone please give me the answers to this question. Explanation is not nessecary. i just need to verify my answers. thanx
$S_y = u_yt - \frac12 gt^2$
$-100 = (200\sin 20^{\circ})t - \frac12 g t^2$
$\implies t=15.29, \ -1.33$
Time cannot be negative hence $t= 15.29s$

$S_x = u_xt$
$S_x = (200 \cos 20^{\circ})(15.29) = 2874m$

EDIT: Drawing a diagram for these type of question does help.

3. Originally Posted by Air
$S_y = u_yt - \frac12 gt^2$
$-100 = (200\sin 20^{\circ})t - \frac12 g t^2$
$\implies t=15.29, \ -1.33$
Time cannot be negative hence $t= 15.29s$

$S_x = u_xt$
$S_x = (200 \cos 20^{\circ})(15.29) = 2874m$

EDIT: Drawing a diagram for these type of question does help.
You have answered this now, but the correct response would have been to ask the original poster what their answer was, then a simple yes or no would suffice.

That way we minimise the possibility of giving the answer needed for a multiple choice question where the poster is not interested in learning how to solve the problem.

Also if they are honest they already know the solution method so you are wasting effort typing the thing out.

Also, check your calculations, you seem to have lost precision somewhere, so your answer is not correct to the nearest metre.

RonL