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M1 acceleratio f=ma question

1464447919546434130295.jpg hi please can anyone explain why question c is worked out this way :F-0.6g=0.6a ? Not this
Attachment not found
thanks.
Original post by coconut64
1464447919546434130295.jpg hi please can anyone explain why question c is worked out this way :F-0.6g=0.6a ? Not this
Attachment not found
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.
Reply 2
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?
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
Reply 4


What d'you want?
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?
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
Reply 7
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?
Original post by Zacken
But why are you tagging me?


was i right in resolving? :redface:
Reply 9
Original post by coconut64
1464447919546434130295.jpg hi please can anyone explain why question c is worked out this way :F-0.6g=0.6a ? Not this
Attachment not found
thanks.


Original post by Steelmeat
was i right in resolving? :redface:


Don't understand the confusion. What the OP's done in his answer is perfectly fine and gets the correct answer.
Reply 10
Original post by Steelmeat
oh i see well then...


Okay.
Reply 11
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.
Reply 12
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.
Reply 13
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.
Reply 14
This is the mark scheme for the question (7) https://3b0a7b1bc87f5381e60f8f717510b7e3072e9617.googledrive.com/host/0B1ZiqBksUHNYcEVTUFdwYmtsb2c/January%202003%20MS%20-%20M1%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...
(edited 7 years ago)
Reply 15
Original post by coconut64
This is the mark scheme for the question (7) https://3b0a7b1bc87f5381e60f8f717510b7e3072e9617.googledrive.com/host/0B1ZiqBksUHNYcEVTUFdwYmtsb2c/January%202003%20MS%20-%20M1%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.
Reply 16
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.
Reply 17
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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