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Moments - AS Physics Unit 2 HELP :(

Guys I'm extremely clueless on this question http://prntscr.com/79856k
I just simply cannot comprehend moments, I don't know how to approach the questions and which principles to apply. However I do know that Moment = Perpendicular Distance * Force. Also that the sum of clockwise moments = the sum of counter clockwise moments. I just do not know when to use these :frown: Any help would be greatly appreciated!
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rjdoran
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Original post by 1017bsquad
Guys I'm extremely clueless on this question http://prntscr.com/79856k
I just simply cannot comprehend moments, I don't know how to approach the questions and which principles to apply. However I do know that Moment = Perpendicular Distance * Force. Also that the sum of clockwise moments = the sum of counter clockwise moments. I just do not know when to use these :frown: Any help would be greatly appreciated!


b(i) the reaction force (R) is a upwards facing arrow from the ground through the middle of the wheel
b(ii) total anticlockwise moments=total clockwise moments
500*0.7 = f*1.5
(500*0.7)/1.5 = f
= 233N
b(ii) this is the force needed to overcome the 500N weight of the wheel barrow, the only other perpendicular distance from the pivot is R. Therefore the reaction force in the anticlockwise direction equals 500-233= 267N.
Reply 2
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1017bsquad
OP
2
Original post by rjdoran
b(i) the reaction force (R) is a upwards facing arrow from the ground through the middle of the wheel
b(ii) total anticlockwise moments=total clockwise moments
500*0.7 = f*1.5
(500*0.7)/1.5 = f
= 233N
b(ii) this is the force needed to overcome the 500N weight of the wheel barrow, the only other perpendicular distance from the pivot is R. Therefore the reaction force in the anticlockwise direction equals 500-233= 267N.


Thanks bro!, but why is it that you multiplied f by 1.5 and not by 0.8?
Original post by 1017bsquad
Thanks bro!, but why is it that you multiplied f by 1.5 and not by 0.8?


Because you are taking moments about the centre of the wheel, and F is 1.5m from the wheel.
Reply 4
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rjdoran
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Original post by 1017bsquad
Thanks bro!, but why is it that you multiplied f by 1.5 and not by 0.8?


You have got to remember you have to solve the anticlockwise and the clockwise moments as separate entities. The pivot is the wheel, so the perpendicular distance from the pivot to the vertical force (f) is 1.5m. What you are proposing is the perpendicular distance from f to the centre of mass 500N, this is not the moment.
Reply 5
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1017bsquad
OP
2
Original post by rjdoran
You have got to remember you have to solve the anticlockwise and the clockwise moments as separate entities. The pivot is the wheel, so the perpendicular distance from the pivot to the vertical force (f) is 1.5m. What you are proposing is the perpendicular distance from f to the centre of mass 500N, this is not the moment.


Oh riiiiiiiight, I understand a lot better now! However I still find difficulty in some questions such as these where I cannot determine where the pivot would be?
http://prntscr.com/79k07l
I'm assuming I'd use the same principle of Clockwise moments = Anti-Clock wise moments?

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