Question

worksheet 77 activity 1. the water pressure at the bottom of a reservoir dam is 400,000 n/m². what force is exerted on a 50 m² section of the dam? force = m×g 2. a boy standing on one foot exerts a pressure of 65000 n/m² on the ground. if the area of his foot is 0.008 m². a) calculate the total downward force. b) what pressure would he be exerting on the ground if he stands on both feet?

Explanation:

Step1: Recall pressure - force formula

The formula for pressure $P=\frac{F}{A}$, where $P$ is pressure, $F$ is force and $A$ is area. We can re - arrange it to find force $F = P\times A$.

Step2: Solve for the force on the dam

Given $P = 400000\ N/m^{2}$ and $A=50\ m^{2}$. Substitute into the formula $F = P\times A$.
$F=400000\times50 = 20000000\ N$

Step3: Solve for the downward force of the boy (part a)

Given $P = 65000\ N/m^{2}$ and $A = 0.008\ m^{2}$. Using $F = P\times A$.
$F=65000\times0.008=520\ N$

Step4: Solve for the pressure when the boy stands on both feet (part b)

The total downward force $F = 520\ N$. When standing on both feet, the area $A_{new}=2\times0.008 = 0.016\ m^{2}$. Using $P=\frac{F}{A}$, we have $P=\frac{520}{0.016}=32500\ N/m^{2}$

Answer:

1. The force on the dam is $20000000\ N$.
2. a) The total downward force of the boy is $520\ N$.

b) The pressure when the boy stands on both feet is $32500\ N/m^{2}$.