Crate Friction on Horizontal Floor

[VinnyCee]

I have a problem with an answer that I don't know how to arrive at.

There is a 35 kg crate on a horizontal floor that a person is pushing with a 110 N force. The coefficient of static friction is 0.37. What is the maximum value f of s, max for which the crate will not move?

I thought that the answer is f of s, max = (coefficient of static frction)(35 kg)(9.8 m / s^2) = 127 N. However, the book lists an answer of 130 N. Am I going about his problem correctly?

[BLaH!]

You're absolutely correct! f_{s, max} = \mu_s N = \mu_s mg Because there are only 2 significant digits in the values for m, \mu_s etc., the answer should be expressed with only 2 significant digits. You got an answer of 127 N which contains 3 significant digits. The book simply rounded up to 130 N to express the answer in 2 significant digits. Wasn't that simple? You were doing everything correctly!

[VinnyCee]

Thank you for the reassurance! I don't think I would have gotten any further in the assignment stressing over that one little answer! :redface: