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# M1 acceleratio f=ma question

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1. hi please can anyone explain why question c is worked out this way :F-0.6g=0.6a ? Not this Attachment 539993539997 thanks.
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2. (Original post by coconut64)
hi please can anyone explain why question c is worked out this way :F-0.6g=0.6a ? Not this Attachment 539993539997 thanks.
don't you use F=ma in the direction of acceleration?
in which case the ball is slowing down thus acceleration is in the upwards direction.
3. (Original post by Steelmeat)
don't you use F=ma in the direction of acceleration?
in which case the ball is slowing down thus acceleration is in the upwards direction.
But the ball is decelerating downward though. So f=ma would be downward right?
4. (Original post by coconut64)
But the ball is decelerating downward though. So f=ma would be downward right?
i'm sure you take the direction of acceleration as positive so when you find the resultant force you resolve upwards, downwards doesn't matter either

upwards you get F-0.6=0.6a
downwards you get 0.6-F=-0.6a i think

Zacken
5. (Original post by Steelmeat)
Zacken
What d'you want?
6. (Original post by coconut64)
But the ball is decelerating downward though. So f=ma would be downward right?
You can do it eitherway if you specify which way is positive? If down is positive then restive force is negative and acceleration is negative, the other way and resistive force is positive and acceleration is positive?
7. (Original post by Zacken)
What d'you want?
Op doesn't understand that you resolve in the direction of acceleration :/
or define which direction is positive
8. (Original post by Steelmeat)
Op doesn't understand that you resolve in the direction of acceleration :/
or define which direction is positive
But why are you tagging me?
9. (Original post by Zacken)
But why are you tagging me?
was i right in resolving?
10. (Original post by coconut64)
hi please can anyone explain why question c is worked out this way :F-0.6g=0.6a ? Not this Attachment 539993539997 thanks.
(Original post by Steelmeat)
was i right in resolving?
Don't understand the confusion. What the OP's done in his answer is perfectly fine and gets the correct answer.
11. (Original post by Steelmeat)
oh i see well then...
Okay.
12. (Original post by Zacken)
Don't understand the confusion. What the OP's done in his answer is perfectly fine and gets the correct answer.
Hi guys, I actually got it wrong. It is actually a 'her' not 'his' btw. Anyway, the right answer is 6390N ;however mine is 6380N to 3sf. And also my positive direction is downward so 0.6g which is acting downward would be postive and F is negative. Thanks.
13. (Original post by Steelmeat)
Op doesn't understand that you resolve in the direction of acceleration :/
or define which direction is positive
I did mention that I have taken the downward direction as positive, so 0.6g is positive. Thanks.
14. (Original post by Middriver)
You can do it eitherway if you specify which way is positive? If down is positive then restive force is negative and acceleration is negative, the other way and resistive force is positive and acceleration is positive?
Hi, my positive direction is downward, and I did use -F in my answer. My working which I have uploaded is 0.6g-F=o.6a. Thanks.
15. This is the mark scheme for the question (7) https://3b0a7b1bc87f5381e60f8f717510...%20Edexcel.pdf. I got v as 23.04.... which if I round it would give me 23.05. So for acceleration I got -10623.2 instead of a = –10644.5. Why are there two different values for v though? I got 23.0469 but the mark scheme used 23.07...
16. (Original post by coconut64)
This is the mark scheme for the question (7) https://3b0a7b1bc87f5381e60f8f717510...%20Edexcel.pdf. I got v as 23.04.... which if I round it would give me 23.05. So for acceleration I got -10623.2 instead of a = –10644.5. Why are there two different values for v though? I got 23.0469 but the mark scheme used 23.07...
I disagree with their answer, see question 50 here. In either case, looks like a simple rounding issue than anything else, your method is correct.
17. (Original post by Zacken)
I disagree with their answer, see question 50 here. In either case, looks like a simple rounding issue than anything else, your method is correct.
Okay but just wondering why is the answer like that in the marks scheme and there are two different answers for v? Thank you.
18. (Original post by coconut64)
Okay but just wondering why is the answer like that in the marks scheme and there are two different answers for v? Thank you.
Like I've said before: rounding issue. They used the rounded version of T which made them inaccurate.

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