Monday 28 September 2015

homework and exercises - Based on newtons third law



If an elephant can apply 250N force and a rabbit can apply 25N force , and if they are pulling each other , then elephant will pull with 250N force and according to newtons third law the rabbit should also pull the elephant with 250N force.then from where do the rabbit got the extra 225N i.e.(250-25=225) force??? can anyone please explain.



Answer



To check your data image that a spring balance was connected to a wall and the elephant and the rabbit were asked to pull as hard as they could so that you could take a reading of their maximum pulling force.
What that reading will show is the maximum horizontal force that the elephant and the rabbit can exert on the ground with their feet.
This is because when the elephant pulls on the spring balance the spring balance pulls on her with an equal force. (N3L)
For the elephant not to move the ground must push the elephant with an equal force so that the net force on the elephant is zero. (Not N3L)
So the maximum pull is the maximum horizontal push that the feet can exert on the ground which is equal and opposite to the maximum push the ground can exert on the feet. (N3L)


So now we come to the tug of war.

The rabbit pulls with a force of 10 N and the elephant also pulls with a force of 10 N. There is not a lot of movement. The rabbit then pulls with a maximum force for him of 25 N and the elephant counters with a force of 25 N. Stalemate again.


The elephant now pulls with a force greater than 25 N, a force which is greater than that which the ground can exert on the rabbit.
There is thus a net force on the rabbit.
So the rabbit accelerates towards the elephant.


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