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

  • Thread starter nrc_8706
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  • #1
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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)
 

Answers and Replies

  • #2
VietDao29
Homework Helper
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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,
 
  • #3
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thanks

thank you viet dao, i figured it out.
 
  • #4
71
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?

but now how do you find max height?
do u use y=voyt + 1/2gt^2?
 
  • #5
VietDao29
Homework Helper
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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:
vf2 = vi2 + 2ad
Here a = -g (if you choose the positive direction upward).
vi is the object's initial velocity.
vf is the object's final velocity.
Here, you just need the y-component, so the vi is the y-component of the initial velocity.
vf = 0 m / s. It's when the object's velocity has no more y-component.
You can use that and solve for d, which's the object's max height.
Viet Dao,
 

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