physical

A 0.8 kg block of wood has an initial velocity of 0.25 m/s as it begins to slide across a table. The block comes to rest over a distance of 0.72m.
a) what is the average frictional force on the block?
b)How much work is done on the block by friction?
c)How much work is done on the table by the block?

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1. avg acceleration=frictionforce/mass

Vf^2=Vi^2+2a*distance

Vf^2=Vi^2+2*frictionforce/mass * distance

solve for friction force.

work=force*distance

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2. But if i do this for force of friction, the result of frictional force is going to be negative. :(

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