A load weighing 1500 N is at a height of 5 m above a pole with a weight of 7500 N and the pole upright on the ground. If the load is released and mashing the pole, then the pole will go into the ground as far as 25 cm. Calculate the soil resistance force.

Question

anonymous · Answer

Can I use conservation of momentum?

anonymous · Answer

I don't think that's the right way to go.  Conservation of energy will probably work better.

$$ E_i = E_f
\ U_i + K_i = U_f + K_f + W_{NC} $$

then your nonconservative work will be equal to your resistance force times the distance pushed into the ground.  ^^

anonymous · Answer

Are we assuming that the resistance stays the same? Anyways even if it doesn't I think the average force will still be the same as long as resistance is directly proportional with the distance the rod is stuck into the soil. Take a look at the attached file for my work.

anonymous · Answer

thanks to you both ^^

@AllTehMaffs does it not apply at all? or it was maybe to used but not the better ways?

anonymous · Answer

I mean, conservation of momentum HAS to hold if you define your system well enough, and you could probably set it up if you really, really wanted to.  But it would be awful.  What would the final mass of the inelastic collision be?  the block plus the pole plus the earth? Plus the block is being accelerated, so that complicates things too.  A mess.  It'd be a mess.

anonymous · Answer

You could totally try and set it up though - never let me tell you you can't do something.  I'm just lazy and energy is easier ^^

anonymous · Answer

***it would be awful***

anonymous · Answer

well, I understand. I just ask, because my teacher use it to solve this problem. :D
thank you ^^

anonymous · Answer

I'm super curious as to how your teacher did that then! :)