2 Projectile Questions (1 Viewer)

[kubekoo]

I can do most of the questions, but when question involve unknow value of V (the initial velocity) and alpha or theta (the initial angle of projection) then i have fully lost...

Like for those questions, I can find expression for time of flight , range, maximum height etc... but they are all in terms of V and alpha ... any one know how to get rid of them.. cos answer @ the back of the book is number alone... without V and alpha...



anyways... these are the examples questin i got stuck.. hope someone here can give me a hand...

From Jones and Couchman...
Ex26.4

Q6.
A boy can throw a stone a maxiumu horizontal distance of 80m. How long is the stone in the air and to what height does it rise?

Q10.
At the highest point of its path a body has a velocity of 10m/s and 8m above the ground. Find the angle of projection and the initial velocity.

(just one questino abt Q10~ it says @ the highest position, it has velocity of 10m/s ..... since @ highest point, vertical velocity is zero right? so 10m/s should be only coming from the horizontal velocity, so 10=V(cos alpha) ??)



i actually have more... but i fink they are around the similar format... so in anyone can give me a hand on these few quesitons, then i can try the rest myself......

Thanks you very much...

 

[shafqat]

range = 2v^2sin@cos@/g
= v^2sin2@/g
This is max when sin2@ = 1, because thats the maximum this sine function can be.
so max range = 80 = v^2/g
so now you know v.

your assumption abt q10 is correct.

 

[shafqat]

if you need further help on 10:

you will get two expressions, Vsin@ and Vcos@. Divide and therefore calculate tan@. Then sub @ back in for V.

 

[kubekoo]

Kooooooooooool.......... i understand Q6 now.....

Got out Q10 too~~ thx thx~~~~~~~~!