Why is it necessary to bend knees while jumping from a height?
Asked Rahul. (via SMS from our mobile version http://m.askphysics.com )
This is a consequence of the impulse momentum principle.
When we bent our knees on landing, the time of impact increases and reduces the average force exerted during the entire process. This prevents the chance of damage to our body.
Impulse momentum principle states that the impulse of a force is equal to the change in momentum produced.
Impulse is measured as the product of force and time interval. So, when we stop ourselves, there is a fixed change in momentum. If we stop ourselves very fast, the time interval is less and the average force will be very large.
But, if we bent our knees during landing, the time involved in the proces of landing will be more and thus the average force will be less and hence the damage will also be less.
What is centripetal force?
Received via SMS from our mobile version of this site http://m.askphysics.com
Centripetal fforce is the net force to be acting on a body so that it can move in a curved path. The centripetal force is always directed towArds the center of the circular path. The word centripetal means “directed towards the center” or “center seeking force”.
Please remember that it is not a new kind of force, but in different case one or more of the fundamental forces or their components provide the necessary centripetal for e.
The magnitude of the centrifugal force that must be acting on a body of mass m moving with a speed v along a curve of radius of curvature r is given by F = mv^2/r
I read in one of my chapters that when a body is immersed in a container of water (kept on a weighing machine which reads ‘W’ at first )the apparent weight lost by the body is equal to the buoyant force, and thus the reading ‘W’ increases.
Then I came across a question like this -
A beaker containing water kept on a weighing machine weighs W. A body of weight ’w’ is dropped in it. It is floating & experiencing a buoyant force B, then the reading on machine is -
please give me the answer and explanation
the book says answer is (a)
but I think it is (c)
(Anwesha posted this questions)
The answer is A.
The total force acting downwards is W+w and the weighing scale is providing an equal reaction. the normal reaction offered by the weighing scale is what we get as the reading.
therefore the reading on the weighing scale must be W+w
The buoyant force is acting on the object dropped and is not contributing to the normal reaction offered by the weighing scale.
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The following questions were posted by Nabeela. We are just posting the question as such so that the visitors can post the answers.
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