Force and pressure answer key

Practice

1. 6 Pa. Divide 18 N by 3 m².
2. 28 N. Force = pressure × area = 14 × 2.
3. 0.30 m². Area = force ÷ pressure = 90 ÷ 300.
4. The girl’s push is a contact force. Gravity is a non-contact force.

Apply

5. 800 Pa on 0.06 m² and 3,200 Pa on 0.015 m². The smaller face gives four times the pressure.
6. The wider strap. Its pressure is 72 ÷ 0.024 = 3,000 Pa, compared with 72 ÷ 0.012 = 6,000 Pa.
7. 20,000 Pa. Each foot supports 160 ÷ 4 = 40 N, and 40 ÷ 0.002 = 20,000 Pa.
8. Before: 50 ÷ 0.10 = 500 Pa. After: (50 + 25) ÷ 0.10 = 750 Pa. The contact area stays the same.

Challenge

9. At least 360 ÷ 1,200 = 0.30 m² in total. Each foot needs at least 0.30 ÷ 4 = 0.075 m².
10. They produce equal pressure: 120 ÷ 0.04 = 180 ÷ 0.06 = 3,000 Pa. The increase in area balances the increase in force.
11. It becomes four times greater. Doubling the force doubles the pressure, and halving the area doubles it again.
12. The lower hole. It is at a greater depth, so the water pressure at that hole is higher.