# Projectile Question Help

Watch
Announcements
Thread starter 7 years ago
#1
In a castle, overlooking a river, a cannon was once employed to fire at enemy ships.

One ship was hit by a cannonball at a horizontal distance of 150 m from the cannon.

The height of the cannon above the river was 67 m and the
cannonball was fired horizontally.

a)Show that the time taken for the cannonball to reach the water surface after being fired from the cannon was 3.7 s. Assume the air resistance was negligible.

b)Calculate the velocity at which the cannonball was fired.

c)Calculate the vertical component of velocity just before the cannonball hit the ship.

For a) Resolving vertically u = 0

So s= ut + 1/2at2

s=1/2at2

67=1/2*9.81 * t2

t = 3.7

I get this.

But for b)

How do I know whether to calculate horizontally or vertically. If horizontally I can do it because a=0 so s=vt but how would I know.

Any help will be greatly appreciated.
0
7 years ago
#2
Note that in the question it says "the cannonball was fired horizontally". Thus there is no vertical component at t=0 only a horizontal component.
1
Thread starter 7 years ago
#3
(Original post by soup)
Note that in the question it says "the cannonball was fired horizontally". Thus there is no vertical component at t=0 only a horizontal component.
Thank you
0
1 year ago
#4
My man, X = Xu * t So Xu = X/t Xu = 67 / 3.7 Xu is the initial horizontal velocity X horizontal distance T is time
0
1 year ago
#5
(Original post by Yazanadi)
My man, X = Xu * t So Xu = X/t Xu = 67 / 3.7 Xu is the initial horizontal velocity X horizontal distance T is time
u do realise that this thread is 6 years old
0
X

new posts
Back
to top
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### Poll

Join the discussion

#### Have you experienced financial difficulties as a student due to Covid-19?

Yes, I have really struggled financially (56)
17.23%
I have experienced some financial difficulties (92)
28.31%
I haven't experienced any financial difficulties and things have stayed the same (122)
37.54%
I have had better financial opportunities as a result of the pandemic (44)
13.54%
I've had another experience (let us know in the thread!) (11)
3.38%