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Forces and Vectors please help :)

May someone check my working for the question attached below please?

F = ma
(5i + 6j) + (2i - 2j) - (-i - 4j) = 7m
7i - 4j - (-i - 4j) = 7m
8i + 8j = 7m
m = (8/7i + 8/7j) kg
(edited 2 years ago)
Screenshot 2021-05-17 at 20.55.00.png53.1KB
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mqb2766
21
Original post by NaBrO
May someone check my working for the question attached below please?

F = ma
(5i + 6j) + (2i - 2j) - (-i - 4j) = 7m
7i - 4j - (-i - 4j) = 7m
8i + 8j = 7m
m = (8/7i + 8/7j) kg

You sum all 3 forces (why add two and subtract one) to get the net force vector.

It makes no sense for a mass to be a vector?
(edited 2 years ago)
Original post by NaBrO
May someone check my working for the question attached below please?

F = ma
(5i + 6j) + (2i - 2j) - (-i - 4j) = 7m
7i - 4j - (-i - 4j) = 7m
8i + 8j = 7m
m = (8/7i + 8/7j) kg

The resultant force is the sum of all the forces so you should add the 3rd one, not take away. Also, mass is a scalar quantity, not a vector (since mass can't really have a direction :tongue:), so you should combine your i and j components at the end to get your answer (if need be). :smile: Hope this helps.
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NaBrO
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Original post by mqb2766
You sum all 3 forces (why add two and subtract one) to get the net force vector.

It makes no sense for a mass to be a vector?

Ok, now I get m = 7/6 kg.
I thought that since the particle is accelerating, it would accelerate to the right since the vectors in the lower and upper right quadrants are bigger than the other vector. I think I see the flaw in that - both of those vectors are going in separate directions?
Reply 4
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mqb2766
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Original post by NaBrO
Ok, now I get m = 7/6 kg.
I thought that since the particle is accelerating, it would accelerate to the right since the vectors in the lower and upper right quadrants are bigger than the other vector. I think I see the flaw in that - both of those vectors are going in separate directions?

Nope, try again m = ...
Also the question asks for 2dp
(edited 2 years ago)
Reply 5
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NaBrO
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Original post by mqb2766
Nope, try again m = ...

6/7 kg ....
Reply 6
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mqb2766
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Original post by NaBrO
6/7 kg ....

Yes, but question says 2dp.

The question is slightly ambiguous about acceleration. However, the force and acceleration vectors only have one non-zero component.
(edited 2 years ago)
Reply 7
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NaBrO
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Original post by mqb2766
Yes, but question says 2dp.

The question is slightly ambiguous about acceleration. However, the force and acceleration vectors only have one non-zero component.

Thanks for the help.

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