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# M2 Help: Watch

1. Hi could someone check my working and tell me if it is right. Also could someone please explain how to do the last part of part four of the question. Thanks

Here's my working:

1) (i)

Taking Moments about A

Clockwise (moments) = Anticlockwise (moments)

80 x 1.5 = 2.5 C

C = 48N

1) (ii)

Clockwise (moments) = Anticlockwise (moments)

80 sin(60) x 1.5 = 2.5C

C = 41.57 N

1) (iii)

Clockwise (moments) = Anticlockwise (moments)

1.5 x 80sin(60) = (20x3)+2.5C

C = 17.57 N

1) (iv)

Clockwise (moments) = Anticlockwise (moments)

1.5 x 80sin(60) = 3T sin 50

T = 45.22 N

Not too sure how to do the very last part of the question. Any help would be very much appreciated
2. I haven't checked your numbers, but your methods are sound.

For the last part, resolve vertical forces - the weight, the slightly upwards force at the hinge, and the slightly upwards force at B.
3. If it's hinged the reaction force isn't perpendicular to wall, it's at an angle, so you can work out the horizontal and vertical components of the force, then use pythagoras and trig to work out the magnitude of the force and the angle at which it acts.

As it's only asking for the vertical, you don't need to use pythahoras and trig, on your diagram just add at vertical force (Y) and horizontal force (X) on your diagram, and work them out as usual

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Updated: December 1, 2010
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