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M2

Stuck again..
I'm getting really confused with work done and conservation of energy and when to use the equations.

A particle of mass 0.2kg is at rest 3m from the edge of a horizontal bench. It recieves an impulse of magnitude 4N
a) P begins to move at speed 20
b) work done against friction is 2.352
c) speed of P as it reaches the edge of the bench
is this just KE=work done?

d)the surface of the bench is 1m above a horizontal floor-calculate the speed with which P hits the floor- is this a projectile or am I using work/energy again?

Thanks :smile:
(edited 11 years ago)
I just realised I need to have work done=0.5m(Intial speed^2-Final speed^2)

BUT WHY??
How would I know if intial KE was greater than final KE or not ??
So confused T__________T
Original post by the.cookie.monster
I just realised I need to have work done=0.5m(Intial speed^2-Final speed^2)

BUT WHY??
How would I know if intial KE was greater than final KE or not ??
So confused T__________T


Energy before = energy afterwards + work done.

Since we're only dealing with kinetic energy and work done against friction, clearly the initial KE must be greater
Original post by ghostwalker
Energy before = energy afterwards + work done.

Since we're only dealing with kinetic energy and work done against friction, clearly the initial KE must be greater


Sorry, I still don't quite understand :/
Original post by the.cookie.monster
Sorry, I still don't quite understand :/


In this case we have:

Kinetic energy before = kinetic energy afterwards + work done.

And since the work done is positive, then the kinetic energy afterwards, must be less than the kinetic energy before.

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