Physics Help

[GunnerVIII]

When I did this question I got an answer that seemed a little off. Im not sure if I did something wrong or this was infact the correct answer, anyway the question was:

 

A rifle can fire a bullet at 1000ms-1. If it is fired vertically into the air, what is the maximum height reached? For how long is it in the air?

 

I worked out that,

 

u=1000ms-1

v=0

a=-9.8ms-2

t=?

s=?

 

I worked out the time first using v=u+at

 

0=1000-9.8.t

and I got 102 sec

 

I then worked out the maximum height reached using s=ut+1/2at^2

s=1000.102+1/2.-9.8.102

and I got 51,021 m

 

Did anyone else get the same answer or have I done something wrong?

 

Thanks

[greg1917]

yeah. different ways to do it.

 

since v^2 = u^2 + 2as

 

you can rearrange to give s = (v^2 - u^2) / 2a

 

which gives 51020m which is close enough to ure figure.

 

and yeah v = u + at which gives t as 102s.