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fusilli_jerry89

Member

Registered: 2006-06-23

Posts: 86

Easy Physics

I don't know if anyone solves physics problems here, but I havn't done this in over a year and can't concentrate right now so I need help.

A 1.2 kg book is given a shove at 2.0 m/s. It slides across the table coming to a stop ).67 metres later. a) what is the magnitude of the force that stops the book? b) What is the coefficient of kinetic friction between the book and table and c) If released at the same speed, would a heavier book slide the same distance? Explain

Last edited by fusilli_jerry89 (2006-10-02 13:58:04)

luca-deltodesco

Member

Registered: 2006-05-05

Posts: 1,470

Re: Easy Physics

youd be better off here for physics questions

http://www.ilovephysics.com/forum/

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mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: Easy Physics

Ah, don't worry. That question's fine here as well. Physics and maths are very closely related, and that question looks like it would be more suitable in a maths test than in a physics test anyway.

a) First we need to work out the kinetic energy that the book has initially.
This is 1/2mv², which in this case is 0.5*1.2*2², which is 2.4J.

Now we know that 2.4J of energy was used to stop the book, so we can use that Energy = Force x distance.

2.4 = Force * 0.67
Therefore, Force = 2.4/0.67 = 3.6N.

b) Frictional force = μR, where μ is the coefficient of friction and R is the reaction of the table on the book.
As the table is flat, R is the same as the weight of the book, which is 1.2g = 11.76N.

So now we have 3.6 = μ*11.76, meaning μ = 3.6/11.76 = 0.306, to 3 significant figures.

c) A heavier book would slide the same distance as before because it would have more initial energy, but there would also be a greater frictional force slowing it down, so the two cancel out.

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fusilli_jerry89

Member

Registered: 2006-06-23

Posts: 86

Re: Easy Physics

is there a way to get the Force of friction without using conservation of energy? like just newton's laws for example?