Pressure

On a frozen lake, the ice will break if the pressure on it is greater than 1 N/cm².

Four boys stand on the ice.

Which one will fall through?

• Weight 200 N, Area of feet 270 cm²

• Weight 300 N, Area of feet 250 cm²

• Weight 400 N, Area of feet 500 cm²

• Weight 500 N, Area of feet 560 cm²

A 1.5 N rectangular block of wood is placed on a table.

It has a dimension of 6.0 cm by 5.0 cm by 10.0 cm.

What is the smallest possible pressure that the block can exert on the table?

• 0.005 N/cm²

• 0.05 N/cm²

• 0.03 N/cm²

• 0.025 N/cm²

Which of the following examples has the highest pressure exerted?

• An elephant standing on the ground.

• A knife cutting a piece of meat.

• A barefooted person standing on the bench.

• A book resting on a table.

A boy is trapped in a large area of very soft mud. A man rescues the boy by crawling across a long, light board rather than by walking into the mud.

What effect, if any, does the use of the board have on the the pressure on the mud, compared with walking?

• increased pressure

• decreased pressure

• no change

The figure shows a battle tank of weight 150 000 N. It uses tracks instead of wheels.

The pressure exerted on the ground is 25 kPa.

Calculate the contact area of the battle tank with the ground.

• 6 m²

• 6 000 m²

• 3 750 000 m²

• 3 750 000 000 m²

Two closely-fitted smooth pistons are connected as shown below.

A force of 3N applied on the 2 cm2 piston causes a pressure. The liquid transmits the pressure to the 6 cm2 piston, where force X is exerted.

What is the magnitude of force X that is needed to balance the system?

• 1.5 N

• 3 N

• 6 N

• 9 N