Simple Problem, (well i say simple...)

benhorris

Heres a question for you, cant work out what formula to use so i need some help.

A mass of 220KG, hits a cylindrical pole into the ground. Just before it hits the velocity of the mass is 10ms-1.

The pole is pushed 0.4 m into the ground, when the mass is droped 5m onto the pole. G = 9.8ms-2.

Show that the average force exerted by the pole on the mass is 27kN.

I just cant work it out! i know its simple but if someone can explain it to me id much appreciate it as ive spent nearly 30 mins on this one question and its only worth 2 marks..

Thanks in advance.

Ben.

dextercioby

Presumably there's no friction between the pole & the mass,so u'll have to assume that the force required will do work in pushing the pole.So the work done is equal to the KE transferred by the mass.

Daniel.

benhorris

KE =0.5mv^2

hence 0.5x220x100 = 11000 J

????? Now what - stuck on this Q and its very annoying...

dextercioby

Yes,but for a collinear force,the work is simply W=F*d...

Daniel.

benhorris

Arnt i a numpty.... hehe.

W=f*D
11000/0.4 =f

f =27500N

Duh, flippin ek. Always the simple ones that get me..

benhorris

Thanks by the way. Im sure i have tested your intellectual capabilities to the utmost extreme levels. ....

;-)

Thanks once again.

dextercioby

Don't worry,i had the head-ache before looking over your problem... It's just that now,i suddenly feel it more intensely...

Daniel.

P.S.OUCH!!