pressure (topic 5)

Question 1

describe how the pressure exerted on the table would change when the block is placed with the smaller face on the desk (2)

Answer 1

• pressure would increase
• same force exerted over a smaller area

Question 2

explain why the pointed tip of a nail makes it easier to hammer into a piece of wood (2)

Answer 2

• pressure increases
• force spread over a smaller surface area when pointed

Question 3

as the hammer strikes the nail, the nail exerts a force on the wood, the wood also exerts a force on the nail, explain why (2)

Answer 3

• Newton’s third law
• all forces create an equal and opposite reaction force

Question 4

the student claims that the pressure exerted on the desk would be greater in granulated form because more of it would be in contact with the desk, explain why the student is wrong (3)

Answer 4

• the total force exerted on the desk is the same as the mass of sugar is the same
• the surface area in contact with the desk is greater
• pressure is lower as the force is spread over a larger area

Question 5

state the equation linking pressure difference, density, height and gravitational field strength

Answer 5

pressure difference = density x gravitational field strength x height

Question 6

the students predict which of the four containers will have the deepest liquid level when water is added, comment on the students predictions, you should refer to ideas about pressure in your answer

Answer 6

• all students are incorrect
• the pressure is the same for all containers
• pressure = density x gravitational field strength x height
• all container will have the same depth of fluid

Question 7

explain how the water path of C changes as the water drains out (3)

Answer 7

• as water drains from the water column, the height of water above C decreases
• pressure at C decreases
• decreasing force on water leaving at C
• distance travelled by water leaving at C reduces

Question 8

the liquid in the open end of the manometer begins to rise, explain what happens to the pressure of the trapped gas (4)

Answer 8

• the volume of gas increases as the water level below falls
• pressure decreases
• or the difference in height of the trapped gas and the open end reduces
• and pressure difference decreases