Tuesday
May 21, 2013

# Homework Help: Physics

Posted by Sarah on Monday, June 15, 2009 at 12:31pm.

The coefficients of static and kinetic friction between a 476 N crate and the ware house floor are 0.615 abd 0.420, repectively. A worker gradually increases his horizontal push against this crate utnil it just begins to move and from them on maintains that same maximum push. What is the acceleration of the crate after it has begun to move?

Netforce=ma
mg(mus-muk)=ma
solve for a

so I got 476 (9.8) (0.615-0.420) = ma

but what is the other m ???

• Physics - drwls, Monday, June 15, 2009 at 12:55pm

There is only one mass, M, and it equals the weight divided by g, which is 48.6 kg.

The equation you wrote is the correct one after motion starts.

The force needed to start it moving is
Mg *(mu,stat) = 292.7 N, After it starts moving, the friction force becomes
Mg*(mu,kin) = 199.9 N
The net accelerating force is then
292.7 - 199.9 = 92.8 N. Divide that by M = 48.6 kg for the acceleration.

• Physics - Sarah, Monday, June 15, 2009 at 1:02pm

so i got 1.91 is the right?

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