# 2 formulas, when do they match...

• Aug 18th 2011, 12:17 AM
Zoognoogle
2 formulas, when do they match...
Hello everyone.
I have 2 formulas, derived from horizontal and vertical position;
V=(4.92t^2 - 1.8)/0.8t
V=√2/0.6t
The question was a projectile motion question to find what velocity a high jumper needed to be travelling at to make a jump of 1.8 metres that was √2 metres away launching at 53degrees. I worked out the 2 positions equations having the same V then created these 2 formulas from there. Not sure what to do from here.. Please help!
• Aug 18th 2011, 04:08 AM
sa-ri-ga-ma
Re: 2 formulas, when do they match...
Check the signs in the first equation.
If you take g negative, h and V*sinθ are positive and the equation becomes
h = V*sinθ*t - 1/2*g*t^2. so the V will be
V=(4.92t^2 + 1.8)/0.8t
• Aug 18th 2011, 09:55 PM
Zoognoogle
Re: 2 formulas, when do they match...
Okay so i have those signs switched, said they equal each other, but i cant seem to get a t value?
• Aug 19th 2011, 01:31 AM
sa-ri-ga-ma
Re: 2 formulas, when do they match...
V=√2/0.6t = (4.92t^2 + 1.8)/0.8t

√2*0.8t/0.6t = (4.92t^2 + 1.8)

√2*0.8/0.6 = (4.92t^2 + 1.8)

Now solve for t.
• Aug 19th 2011, 02:49 PM
Zoognoogle
Re: 2 formulas, when do they match...
Got it thanks :) Discovered my problem was just rounding too much, so when i solved i always got t=0..