Questions on Pressure and Moments
Q102.
(a) James is cutting a piece of wire with a pair of wire cutters.
James exerts a force of 50 N on each of the handles.
(i) What is the turning moment about the pivot, on each handle?
Moment = Force x perpendicular distance from the pivot
Moment = 50 N x 9.0 cm
Moment = 450 
N cm
(2 marks)
(ii) What force is applied, by each blade, on the wire?
Moment = Force x perpendicular distance from the pivot
450 N cm = F x 1.5 cm
F = 450/1.5
F = 300 N
(1 mark)
(b) Stephanie uses a pair of wire cutters. The diagram below is an end-on view of the blades as they begin to cut the wire.
Stephanie exerts a force of 200 N on the wire with each blade.
The area of contact of each blade on the wire is 0.0005 cm2.
(i) What is the pressure of each blade on the wire?
P = F/A
P = 200 N / 0.0005 cm2
P = 400 000 N/cm2
(2 marks)
(ii) As the blades sink deeper into the wire, the pressure of the blades on the wire decreases. Explain why this happens.
Because as the blades sink deeper into the wire the area of contact will increase and as pressure is force divided by contact area that will make the pressure decrease.
(2 marks)
Maximum 7 marks
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