Projectile motion problem

• Nov 12th 2012, 12:30 PM
kinhew93
Projectile motion problem
Hi I just need to see how to approach a problem like this.

A darts player throws a dart at a dart board which hangs vertically. The motion of the dart is modelled as that of a particle moving freely under gravity. The darts move in a vertical plane which is perpendicular to the plane of the dart board. A dart is thrown horizontally with speed 12.6 m s^-1. It hits the board at a point which is 10cm below the level from which it was thrown.

Find the horizontal distance from the point where the dart was thrown to the dart board.

Thanks!
• Nov 12th 2012, 12:34 PM
MarkFL
Re: Projectile motion problem
Hint: Find the time it will take an object to freely fall 10 cm under the influence of gravity, then use distance = speed times time to find the horizontal distance.
• Nov 12th 2012, 01:38 PM
kinhew93
Re: Projectile motion problem
Yeah I did that but my teacher said the answer was wrong...

Could someone show the working for it?
• Nov 12th 2012, 02:54 PM
skeeter
Re: Projectile motion problem
Quote:

Originally Posted by kinhew93
Yeah I did that but my teacher said the answer was wrong...

Could someone show the working for it?

I have a better idea ... you show your working so maybe someone can spot your mistake, or confirm that your solution is correct.
• Nov 13th 2012, 03:07 AM
kinhew93
Re: Projectile motion problem
Ok here's what I did

Finding vertical time:

t^2 = 2(s-ut)/a
= 2s/a
= 0.2/9.8
= 0.0204

so t = 0.14 or 1/7s

Horizontal distance:

s = ut + (at^2)/2
= (12.6 x 1/7) + 0
=1.8m

That seems right to me but maybe not?
• Nov 13th 2012, 03:12 AM
skeeter
Re: Projectile motion problem