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# quick projectiles question- m2 watch

1. hey guys,

In part (b) I don't understand why the vertical displacement would be the same if they were travelling at different speeds and particle A had acceleration.

could someone explain? thanks!
2. (Original post by samantha411)
hey guys,

In part (b) I don't understand why the vertical displacement would be the same if they were travelling at different speeds and particle A had acceleration.

could someone explain? thanks!
I think you've misunderstood. The question is asking you to find the time at which they collide i.e. the time when both objects simultaneously occupy the same position (When they have the same horizontal and vertical displacement).
3. (Original post by Farhan.Hanif93)
I think you've misunderstood. The question is asking you to find the time at which they collide i.e. the time when both objects simultaneously occupy the same position (When they have the same horizontal and vertical displacement).
thanks, i understand now
btw- is this the correct way to post quick maths questions?
Could you also help me out by telling me whether or not there is a normal reaction to the particle at B in this question? (and why)

Thanks once again Farhan.Hanif93!
4. I would think you are just supposed to find the position of the center of mass for the "stone + plank" system. Other than adjusting the CM, you shouldn't need to consider the stone.
5. (Original post by samantha411)
thanks, i understand now
btw- is this the correct way to post quick maths questions?
Could you also help me out by telling me whether or not there is a normal reaction to the particle at B in this question? (and why)

Thanks once again Farhan.Hanif93!
No problem.

Yeah, this is fine. As long as you come in and either ask a very specific question (like you have here) or post some working towards a question that has you stumped then I'm sure someone will be up for helping.

Back to the question, yes there should be a normal reaction force simply because there is contact between two rigid objects. As DFranklin said, you don't actually need to worry about that force for this question.

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