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# Projectile Motion Question! Watch

1. A ball is projected from the ground towards a vertical wall. It strikes the wall at the highest point of its trajectory, 10 metres above the ground. It bounces horizontally away from the wall, with its speed halved by the impact. It lands on the ground at a distance of 20 metres from its original point of projection.

Find the ball’s initial speed and angle of projection.

I know that you will need to use the formulas for the max height and the horizontal range to find the time it takes for the ball to get to the wall, I'm wondering if anyone can verify what value of 't' you get for this since I got 4.472s and I'm not sure if it is correct or not. :/

Can anyone help?
2. Can you show your working? Makes it much easier to verify if your value is right or not.
3. (Original post by As_Dust_Dances_)
A ball is projected from the ground towards a vertical wall. It strikes the wall at the highest point of its trajectory, 10 metres above the ground. It bounces horizontally away from the wall, with its speed halved by the impact. It lands on the ground at a distance of 20 metres from its original point of projection.

Find the ball’s initial speed and angle of projection.

I know that you will need to use the formulas for the max height and the horizontal range to find the time it takes for the ball to get to the wall, I'm wondering if anyone can verify what value of 't' you get for this since I got 4.472s and I'm not sure if it is correct or not. :/

Can anyone help?
I do not get the same value for t when it first hits the wall.

The way I went about it is to call the initial speed x, such that the vertical component of velocity is initially . You can then write an equation for vertical displacement, keeping in mind that the ball reaches 10 metres at its highest point.

At the highest point, the vertical velocity will just be zero, so you can the formula v = u + at with v = 0 to eliminate the unknown value from the displacement equation, which gives t rather quickly.
4. (Original post by As_Dust_Dances_)
A ball is projected from the ground towards a vertical wall. It strikes the wall at the highest point of its trajectory, 10 metres above the ground. It bounces horizontally away from the wall, with its speed halved by the impact. It lands on the ground at a distance of 20 metres from its original point of projection.

Find the ball’s initial speed and angle of projection.

I know that you will need to use the formulas for the max height and the horizontal range to find the time it takes for the ball to get to the wall, I'm wondering if anyone can verify what value of 't' you get for this since I got 4.472s and I'm not sure if it is correct or not. :/

Can anyone help?
At first I would calculate the vertical component of the speed

where h=10 m above the ground. From this

Then calculate the time from

The horizontal distance for t time

After bounce:
for the t2 time

and with t2

And you know that

From this you will get
5. (Original post by Brister)
I do not get the same value for t when it first hits the wall.

The way I went about it is to call the initial speed x, such that the vertical component of velocity is initially . You can then write an equation for vertical displacement, keeping in mind that the ball reaches 10 metres at its highest point.

At the highest point, the vertical velocity will just be zero, so you can the formula v = u + at with v = 0 to eliminate the unknown value from the displacement equation, which gives t rather quickly.
I'm still not quite sure, from this I end up with t = 1.428s? and then I'm not sure where to go from this..
6. (Original post by As_Dust_Dances_)
I'm still not quite sure, from this I end up with t = 1.428s? and then I'm not sure where to go from this..
Next time, please show us some working. Any working will do.

At least give us some nice labelled diagrams. Mathematicians love diagrams.

I have attached my working for this problem.
Attached Images

7. (Original post by Brister)
Next time, please show us some working. Any working will do.

At least give us some nice labelled diagrams. Mathematicians love diagrams.

I have attached my working for this problem.
Thank you, makes a lot more sense now!

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