OCR M2 - Projectiles (pretty tough 11 marker) Watch

Quoz
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#1
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#1
A missile is projected with initial speed 42ms-1 at an angle of 30 degrees above horizontal. Ignoring air resistance, calculate

i) the maximum height of the missile above the level of the point of projection

ii) the distance of the missile from the point of projection at the instant when it is moving downwards at an angle of 10 degrees to the horizontal.

part ii is worth 11 marks, and iv no idea how to go about it. part i) = 22.5m if that helps you.

thanks
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DFranklin
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The horizontal velocity is constant, call it H (as I can't be bothered to do the actual calculation). If it is moving down at an angle of 10 degrees to horizontal, then the vertical velocity is going to be -H tan 10.

Solve for t, then calculate the distance. (I don't know if you're supposed to measure the distance as a straight line or just horizontal distance; in an exam I'd do both).
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Quoz
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why is it tan...?
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DFranklin
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If the particle has position (x,y) where x,y are functions of t, then the gradient = dy/dx. But the gradient is also the angle between the tangent and the horizontal, so we have dy/dx = -tan 10.

Now use \frac{dy}{dx} = \frac{dy}{dt}\frac{dt}{dx} = \frac{dy}{dt} \Big/ \frac{dx}{dt}
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Kyalimers
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Thats all well and good but this is M2 and you're teaching him C3 / C4 methods.
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Hashshashin
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(Original post by sohanshah)
Thats all well and good but this is M2 and you're teaching him C3 / C4 methods.
OCR M2 assumes knowledge of C3/C4.
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Kyalimers
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(Original post by Hashshashin)
OCR M2 assumes knowledge of C3/C4.
Interesting. Edexcel M2 doesn't.
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-G-a-v-
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(Original post by sohanshah)
Interesting. Edexcel M2 doesn't.
I think Edexcel assumes C3 from what I remember.

Besides, who cares? Presumably the OP will have done C3 and C4 now so it doesn't matter where the relevant maths comes from.
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