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# easy m2 question (I'm being dumb)

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1. A particle, of mass 0.4kg, is projected vertically upwards with an initial speed of 30 ms . at time t s after projection, the speed of the particle is v ms and the magnitude of the air resistance acting on the particle is 0.2 vN. Show that -9.8-0.5v = dv/dtIt is only a 2 mark question. I know to use F = ma where a=dv/dt. I can see that 9.8 is obviously gravity but I'm unable to work it into my equation :(-0.2v = 0.4dv/dt will then get you -0.5v =dv/dt but where do I fit the 9.8 in so that it remains unchanged? (Sorry for asking a very simple question ahaha)
2. (Original post by 98matt)
A particle, of mass 0.4kg, is projected vertically upwards with an initial speed of 30 ms . at time t s after projection, the speed of the particle is v ms and the magnitude of the air resistance acting on the particle is 0.2 vN. Show that -9.8-0.5v = dv/dtIt is only a 2 mark question. I know to use F = ma where a=dv/dt. I can see that 9.8 is obviously gravity but I'm unable to work it into my equation -0.2v = 0.4dv/dt will then get you -0.5v =dv/dt but where do I fit the 9.8 in so that it remains unchanged? (Sorry for asking a very simple question ahaha)
You are forgetting the weight of the particle which acts 0.4g Newtons downward.

Your working is correct, but if you consider the weight in addition to the air resistance, you would get:
as required.
3. (Original post by RDKGames)
You are forgetting the weight of the particle which acts 0.4g Newtons downward.

Your working is correct, but if you consider the weight in addition to the air resistance, you would get:
as required.
Thanks I knew it was something stupid and trivial like that ahaha, I feel dumb now
4. (Original post by 98matt)
Thanks I knew it was something stupid and trivial like that ahaha, I feel dumb now
Happens sometimes, I still feel dumb about forgetting something obvious when it comes to problems involving Hooke's Law (as far as M2 is concerned) so I can relate
5. (Original post by RDKGames)
Happens sometimes, I still feel dumb about forgetting something obvious when it comes to problems involving Hooke's Law (as far as M2 is concerned) so I can relate
Rectilinear motion is the first (and only) topic I've looked at in M2 so far. The only bit of Hooke's Law I know is from AS physics aha

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