Questions on Pressure and Moments
Q1. Two syringes are connected together as shown in the diagram below.
A force of 20 N is applied to the piston in syringe A.
(a) Calculate the pressure that the piston in syringe A exerts on the oil.
P = F/A
P = (20 N)/ (0.5 cm2)
P = 40 N cm-2
(3 marks)
(b) Calculate the force needed to just prevent the piston in syringe B from moving out.
P = F/A
So F = PA
F = 40 x 5 = 200 N
(3 marks)
(b) The diagram below shows the brake pedal used to operate the brakes in a car.
The foot applies a force of 50 N.
(i) Calculate the force applied to the piston P.
Moment supplied by the foot = 50 N x 20 cm
Moment = 1000 N cm
1000 N cm = Force applied to piston x 5 cm
Force applied to piston = 1000/5
Force applied to piston = 200 N
(4 marks)
(ii) The brake fluid pushes another piston, Q, which is attached to the car's brakes. Piston Q has an area which is eight times larger than piston P. Calculate the force on the car's brakes.
F = 200 x 8 = 1600 N
(2 marks)
Maximum 12 marks