Why is it necessary to bend knees while jumping from a height?
Why is it necessary to bend knees while jumping from a height?
Asked Rahul. (via SMS from our mobile version http://m.askphysics.com )
Answer:
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.
Related articles
Categories: Mechanics Tags: Business, Central Board of Secondary Education, force, Mathematics, mobile version, Momentum, previous question, SMS
What is centripetal force?
What is centripetal force?
Received via SMS from our mobile version of this site http://m.askphysics.com
Answer
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
Categories: Ask Physics, doubt, Force, Mechanics Tags: centrifugal, centripetal, force
Buoyancy
A pound coin floating in mercury (Photo credit: Wikipedia)
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 -
(a)w+W
(b)W+B
(C)W+w-B
(d)W
please give me the answer and explanation
the book says answer is (a)
but I think it is (c)
(Anwesha posted this questions)
Answer
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.
Related articles
Categories: Ask Physics, Mechanics, Numerical Problems Tags: Buoyancy, Business, Central Board of Secondary Education, Employment, England, Environment, Gairloch, Health, Highland, Industrial Goods and Services, Industrial Supply, Lifejacket, Mackay, Newspaper, Potential energy, Scales and Weighing Equipment, Scotland, Weighing scale, Weight Loss, Wester Ross, wikipedia
Physics Numerical Problems posted by Nabeela
The following questions were posted by Nabeela. We are just posting the question as such so that the visitors can post the answers.
- A mass-less string pulls a mass of 20kg upward against gravity. The string would break if subjected to a tension greater than 400N. What is the maximum acceleration with which the mass can be moved upward?
- A bullet of mass 20g is fired from a gun of mass 10kg with a velocity of 180m/s. Find the velocity of recoil of the gun. Find the force required to stop the gun before it moves 20cm
A body of mass 40kg is moving up an inclined plane with a uniform velocity when a force of 460N is applied. If the plane is inclined to the horizontal by an angle of 45o,calculate the coefficient of kinetic friction between the surfaces.- If the coefficient of friction between the tyres of a truck and the road is k, show that the maximum stopping distance of the truck when moving with a velocity ‘v’ is v2/2 kg. Assume that the brakes are not applied
- A ball of mass 0.5kg moving with a speed of 20m/s collides with an identical ball at rest. After collision the direction of each ball makes an angle of 30o with the original direction. Find the speed of each ball after collision.
- What is the maximum horizontal distance that a ball thrown with a speed of 60 m/s can go without hitting the roof of a long hall 30m high?
- A ball is thrown horizontally strikes a wall 5m away. The height of the point struck by the ball is 1m lower than the height which it was thrown from. (1) With what velocity was it thrown (2) At what angle did the ball reach the wall?
- The time of flight of aprojectile is 10 seconds . its range on a horizontal plane is 100m . Calculate the angle of projection and the velocity of projection.
Related articles
- Numerical Problems from Kinematics (askphysics.com)
- Numericals on Freely falling bodies (askphysics.com)
- Gravity, Balance and some doubts (askphysics.com)
- How does Higg’s Boson transfer mass? (askphysics.com)
