# urgent maths help! M1 as level- projectiles

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Thread starter 5 years ago
#1
Hi,

i need help with one of the questions. I have the answers but i don't seem to get the right answer in the back of the book.

1. A particle is projected with a velocity whose horizontal and vertical components are Vx and Vy respectively. The highest point of its flight is 12m above and 32m horizontally from the point of projection. Find Vx and Vy and hence the initial speed and angle of the particle.

I have an asnwer of 13.07i+24j as my initial speed in vector form
so I have 27.3 m/s as my answer for finding the initial speed but at the back of the book it says it's 20.5m/s, 15.4m/s, 25.6m/s.

How are there 3 initial speeds??
Please help!
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5 years ago
#2
(Original post by liemluji)
Hi,

i need help with one of the questions. I have the answers but i don't seem to get the right answer in the back of the book.

1. A particle is projected with a velocity whose horizontal and vertical components are Vx and Vy respectively. The highest point of its flight is 12m above and 32m horizontally from the point of projection. Find Vx and Vy and hence the initial speed and angle of the particle.

I have an asnwer of 13.07i+24j as my initial speed in vector form
so I have 27.3 m/s as my answer for finding the initial speed but at the back of the book it says it's 20.5m/s, 15.4m/s, 25.6m/s.

How are there 3 initial speeds??
Please help!
Did you read the question?

It asks to find Vx, Vy and HENCE the inital speed. The answers, I assume, are in that order
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Thread starter 5 years ago
#3
(Original post by Student403)
Did you read the question?

It asks to find Vx, Vy and HENCE the inital speed. The answers, I assume, are in that order
Yes I read the question. i found the initial speed in vector form first, then i got 27,3 m/s as my initial speed. But I don't know why it isn't the answer.
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5 years ago
#4
(Original post by liemluji)
Yes I read the question. i found the i found the initial speed in vector form first, then i got 27,3 m/s as my initial speed. But I don't know why it isn't the answer.
Just did it and got the same answers as in the book. Try without using vectors?
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5 years ago
#5
(Original post by liemluji)
Hi,

How are there 3 initial speeds??
Please help!
Velocity is a vector; speed is a scalar.

You have found the velocity in terms of components. Its magnitude is the speed.
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