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# M2 help!! watch

1. Hi can someone please explain to me how to do 6c, thanks.

In case you need it, 6a is 30.4 for 6b it is 68m and the answer for 6c is 3.19.

The main problem I am having with 6c is finding the vertical component of speed at c, on the mark scheme it just says the vertical component is 15/tana
Where 15 is the horizontal speed (25cosa)

Thanks for the help.

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2. The key to this is perpendicular gradients. When the particle is launched from A, its initial "gradient" of flight is given by (vertical component of velocity) / (horizontal component of velocity). You must have worked out these components to answer (a) and (b) so I'm giving nothing away by saying that this initial "gradient" is 20/15=4/3.

The particle will be travelling in a direction perpendicular to the direction at launch when its "gradient", measured the same way is minus the reciprocal of the original gradient. The horizontal component of velocity is constant, so it's quite easy to work out the new vertical component needed to give the required perpendicular gradient. Let's call this V2.

The final step is to use a suitable SUVAT formula to find the time from launch until the vertical component of velocity reaches V2 (which will be negative if you're treating the upwards direction as positive).
3. (Original post by old_engineer)
The particle will be travelling in a direction perpendicular to the direction at launch when its "gradient", measured the same way is minus the reciprocal of the original gradient. The horizontal component of velocity is constant, so it's quite easy to work out the new vertical component needed to give the required perpendicular gradient. Let's call this V2.

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Hi, thanks for the reply, I have worked out the gradient and the -ve reciprocal, the thing that is confusing me is, what should i do with this -ve reciprocal and how exactly would i work out the vertical component from the -ve reciprocal.
thanks
4. You use (new gradient) = (new vertical component) / (constant horizontal component) and rearrange to make (new vertical component) the subject.

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