# Questions on Pressure and Moments

Q2. The diagram shows a simple tool for punching holes in a leather belt.

When the handle is pressed down by a user, the steel peg presses down on the piece of leather.

If the force exerted is large enough, the peg punches through the leather, making a hole.

(a) Calculate the moment (turning effect) of the 50 N force applied to the handle.

Moment = Fd

Moment = 50 N x 10 cm

Moment = 500 N cm

(2 marks)

(b) This moment makes the steel peg press down on the leather. Calculate the force with which the steel peg presses down on the leather.

Moment = Fd

The moment is provided by the person pushing on the handle

500 = F x 4 cm

F = 500/4

F = 125 N

(2 marks)

(c) The next time the punch is used, the steel peg presses down on the leather with a force of 150 N.

The area of the end of the steel peg is 0.1 cm2.

Calculate the pressure that the steel peg exerts on the leather.

P = F/A

P = 150 N/ 0.1 cm2

a mark for recalling the equation for pressure

P = 1500 N/cm2

(3 marks)

(b) The pressure is too small, and the punch does not go through the leather.

How could you change the design of the punch to make it work using the same force on the handle?

Make the area of contact with the leather (the diameter of the tip of the steel peg) smaller.

(As P = F/A the same force will produce a larger pressure)

(1 mark)

Maximum 8 marks