Vector question help A2

Hi,
In the question below i keep checking my working and can't find a mistake with my numbers so i'm assuming my method's flawed?
Thank you

(edited 2 years ago)

Reply 1

mqb2766

The 625 should be 25. The magnitude of a is 5, so a^2 = 25.

(edited 2 years ago)

Reply 2

Rhys_M

Original post by mqb2766

The 625 should be 25. The magnitude of a is 5, so a^2 = 25

But the vectors i'm adding to give the resultant are forces, so i need to equal it to the magnitude of the force, not acceleration, don't I?
(Using f=ma)
If not then why would they give me the mass?

Reply 3

mqb2766

Yes, missed the mass part. Just skim read the acceleration.
What does the model solution give?

(edited 2 years ago)

Reply 4

Rhys_M

Original post by mqb2766

Yes, missed the mass part. Just skim read the acceleration.
What does the model solution give?

There's not a worked solution but the MS just says -7/3 and -3

Reply 5

mqb2766

-3 gives a force of magnitude 5. I guess -7/3 does the same, so your soln is correct, they;ve probably calculated witen the force has magnitude 5.
Note the -3 solution corresponds to a 3 : 4:5 triangle.

(edited 2 years ago)

Reply 6

Rhys_M

Original post by mqb2766

Thank you

Reply 7

Rhys_M

Original post by Rhys_M

Thank you

There's another question of the same type to which I also get a wrong answer VVVV
Do you think the book has a systematic error?

Reply 8

mqb2766

Not sure what the solution is, but your +10 isnt correct.
Sub the book answer and your corrected answer into the F = .. expression and you should be able to work out which is correct?

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Vector question help A2

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