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 board have on the force and the pressure on the mud, compared with walking?
A. force and pressure is decreased
B. force is decreased; pressure is unchanged
C. force is unchanged; pressure is decreased
D. force and pressure is unchanged
answer C is correct. You need to think on that, and understand the role of area in reducing pressure from a force.
The correct answer is A. force and pressure is decreased.
When the man crawls across the board instead of walking directly into the mud, the weight is distributed over a larger area due to the board's surface area. This reduces the force applied to the mud. Additionally, since the force is spread out over a larger area, the pressure exerted on the mud is also decreased. Therefore, compared to walking, the use of the board reduces both the force and pressure on the mud.
To determine the effect of the board on the force and pressure on the mud, let's assess the situation.
When someone walks on a soft surface like mud, their weight creates a downward force. The area in contact with the mud determines the pressure exerted. Walking directly on the mud means that the weight is distributed over a small area, resulting in higher pressure.
When the man rescues the boy by crawling across a long, light board, the weight is still applied to the mud. However, the weight is distributed over a larger surface area due to the board's length. This results in reducing the pressure exerted on the mud compared to walking without the board.
Therefore, the correct answer is:
C. force is unchanged; pressure is decreased