# Denote the initial speed of a cannon ball fired from a battleship

nrc_8706
denote the initial speed of a cannon ball fired from a battleship as Vo. when the initial projectile angle is 45 degrees with respect to the horizontal, it gives a maximum range of R.
the time of flight of the cannonball for this maximum range R is given by
1.t=(1/3^1/2)vo/g
2.t=3^1/2(vo/g)
3.t=2^1/2(vo/g)
4.t=2(vo/g)
5.t=1/2(vo/g)
6.1/(2^1/2)(vo/g)
7.t=4(vo/g)
8.t=(1/4)(vo/g)
9.t=(2/3)(vo/g)

Homework Helper
So, what have you done? Which option to you is correct?
Because you just need to find the time of flight, you don't need the x-component of your initial velocity, you just need the y-component of the initial velocity. So first, you can try to find out the y-component of the velocity.
Then, note that the object has the acceleration of g (downard). Can you find out the time in flight of the object?
Viet Dao,

nrc_8706
thanks

thank you viet dao, i figured it out.

nrc_8706
?

but now how do you find max height?
do u use y=voyt + 1/2gt^2?

Homework Helper
The y-component of the velocity makes the object go up or down.
Because the object has the acceleration of g (downward), so the y-component of the initial velocity decreases, and the object moves upwards slowlier and slowlier, finally when the y-component of the velocity is 0 (m / s). The object's at its max height, because, right after that, it will start accelerate downwards (ie, it no longer moves upwards).
You can use: