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# M1 mechanics -constant acceleration hwk help watch

1. Hi,

Please could I have some help with these mechanics questions, I am very stuck. For the 1st question I tried to create and solve a simultaneous equation connecting the 2 heights and using T and T+3 for the times of the 2 balls being thrown however I've come out with T being 40 and therefore using S=ut+1/2at^2 a displacement of -7000 which I feel is very wrong!

Thanks
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2. (Original post by VioletPhillippo)
Hi,

Please could I have some help with these mechanics questions, I am very stuck. For the 1st question I tried to create and solve a simultaneous equation connecting the 2 heights and using T and T+3 for the times of the 2 balls being thrown however I've come out with T being 40 and therefore using S=ut+1/2at^2 a displacement of -7000 which I feel is very wrong!

Thanks
Remember that you've defined T as the length of time that B is in the air - it will be important in the question.

What were the simultaneous equations that you made, and how did you solve them?
3. (Original post by SeanFM)
Remember that you've defined T as the length of time that B is in the air - it will be important in the question.

What were the simultaneous equations that you made, and how did you solve them?
Thanks, I've just done question 1 again by equating the equations 25T-5T^2= 25(T-3)-5(T-3)^2 and time came out to be 4 with a displacement of 20(I'm not sure if this is correct but it seems more realistic) for part ii. I realised that the 1st time I accidentally did 120/30 = 40 rather than 4.I'm still stuck with question 2 though
4. (Original post by VioletPhillippo)
Thanks, I've just done question 1 again by equating the equations 25T-5T^2= 25(T-3)-5(T-3)^2 and time came out to be 4 with a displacement of 20(I'm not sure if this is correct but it seems more realistic) for part ii. I realised that the 1st time I accidentally did 120/30 = 40 rather than 4.I'm still stuck with question 2 though
Nice, well done and since you're using T and T - 3 you've defined T as the time A is in the air so you've already got the answer of 4s

For the two time periods, it may help to write out 'S U V A T' and write out what information you've been given, if any, under each letter, and if you don't know them then assign something to them, like for the first one v = v1.
5. Thanks for your help. I've got T=4 so then T-3=1. Then for part ii. I've subbed T=4 into S=uv+1/2at^2 to get displacement as 20m. Is this the right way?

Also I'm stuck on how to do question 2 about the train as I'm not really sure what the best approach is.
6. (Original post by VioletPhillippo)
Thanks for your help. I've got T=4 so then T-3=1. Then for part ii. I've subbed T=4 into S=uv+1/2at^2 to get displacement as 20m. Is this the right way?

Also I'm stuck on how to do question 2 about the train as I'm not really sure what the best approach is.
Woops I gave you a hint for q2 instead of part ii) of question 1, sorry!

And yes, that's fine for part ii)

See my previous post for a hint on q2.

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