Stupid Maths Question

Sinque · 26 Mar 2009 at 18:59

I'm doing revision for my A-Level in Further Maths and i'm in the middle of a mechanics paper and don't understand how it can be done:

'A small stone is dropped from a height of 25metres above the ground. Find the time taken for the stone to reach the ground.'

How is it possible to find the answer with only the displacement and initial velocity?

Vixen · 26 Mar 2009 at 19:00

You have acceleration too...

Sinque · 26 Mar 2009 at 19:02

Vixen said:
You have acceleration too...

Aha, so I do... Thanks for that

Darg · 26 Mar 2009 at 19:07

Doh?

I'd expect a 1st or 2nd year to answer that =/

Hxc · 26 Mar 2009 at 19:08

That's a pretty basic SUVAT question mate... suprised that's in Further Maths, we covered that a while back in Mechanics 1.

Sinque · 26 Mar 2009 at 19:11

Aye, we're doing the exam after Easter - M1 that is. Was just a silly mistake of not remembering acceleration

Vonhelmet · 26 Mar 2009 at 19:12

s = ut + 0.5at^2

25 = 0 * t + 0.5 * 9.8 * t^2

25 = 4.9 * t^2

t = about 2.3

PS Don't bitch if t isn't, in fact, 2.3. I did that last bit in my head.

wonko · 26 Mar 2009 at 19:15

Or if initial velocity<>0
25=ut+0.5x10xt^2 assuming g=10ms-2, no air resistance
gives a simple quadratic to solve.

Vonhelmet · 26 Mar 2009 at 19:16

wonko said:
Or if initial velocity<>0
25=ut+0.5x10xt^2 assuming g=10ms-2, no air resistance
gives a simple quadratic to solve.

Beat you to it.

wonko · 26 Mar 2009 at 19:22

vonhelmet said:
Beat you to it.

Except you assumed initial velocity was 0, which is why I started with "Or if..."