MYP Physics sample question: Pressure, force and area

A student of mass 60 kg stands on both feet. The area of each shoe in contact with the ground is 0.015 m². Take g = 10 N/kg.

1. (a)Calculate the weight of the student.[1]
   Show the mark scheme for (a)

   • • W = mg = 60 × 10 = 600 N (1)
2. (b)Calculate the pressure on the ground when the student stands on both feet.[2]
   Show the mark scheme for (b)

   • • Total area = 0.030 m² and p = F ÷ A (1)
   • • p = 600 ÷ 0.030 = 20 000 Pa (20 kPa) (1)
3. (c)State the pressure when the student lifts one foot.[1]
   Show the mark scheme for (c)

   • • 40 000 Pa (40 kPa), because the area is halved (1)
4. (d)Explain why wearing snowshoes stops a person sinking into soft snow.[2]
   Show the mark scheme for (d)

   • • Snowshoes have a larger area in contact with the snow (1)
   • • The same force spread over a larger area gives a smaller pressure (1)

Remember to add the areas of both shoes, and note that the force (weight) stays the same when the area changes.