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Magazine Chapter 9: Q4 CQ (page 314)
A wrecking ball is being used to knock down a building. One tall unsupported concrete wall remains standing. If the wrecking ball hits the wall near the top, is the wall more likely to fall over by rotating at its base or by falling straight down? Explain your answer. How is it most likely to fall if it is struck with the same force at its base? Note that this depends on how firmly the wall is attached at its base.
Short Answer
The wall when struck by the wrecking ball near the top, it would rotate if the base is not firmly attached.
If the ball strikes the base, the torque is less, the wall can collapse.
Step by step solution
Force
A force is an external factor that can change the rest or motion of a body. It has a size and a general direction.
Explanation of wrecking ball striking the top
When the wrecking ball strikes the wall near the top, it exerts torque about the base of the wall. This torque helps to rotate the wall about its base. The magnitude of the torque increases when the distance of the applied force from the pivot point increases.
This is shown in the diagram below:
Hence, if the wall were firmly attached to the base, the portion that is struck by the ball would break. As the force exerted by the ball would have produced shock waves.
Explanation of wrecking ball striking the bottom
If the wrecking ball strikes the bottom, the torque is negligible as the distance of the applied force from the base is very less. The situation is shown in the figure:
The torque is not sufficient to rotate the wall and the force could knock the base. Hence, the wall can collapse.
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