Calc Push Force Req'd to Move 13g Steel Block on Steel Table

[bjbaldwi]

How much work must you do to push a 13g block of steel across a steel table(coefficent of friction=.6) at a steady speed of 1.2 for 8.8 ?

I know that Work=Force*Distance

i know what the D is but i don't know how to calculate the force.
i tried F=MA and got Fnet= Force pushed -Friction force
i really have no i dea tho. I need help please.

 

[Doc Al]

i tried F=MA and got Fnet= Force pushed -Friction force

Hint: What does 'steady speed' tell you about the net force?

How do you calculate the friction force?

 

[bjbaldwi]

Steady speed says the friction is constant and friction force is kinetic friction*normal force or Fk*mg mg= normal force i think

 

[Doc Al]

OK, good. But what does Fnet equal? (What's the acceleration of the block?)

 

[bjbaldwi]

sorry its 13 kg 1.2 m/s and 8.8 s

 

[bjbaldwi]

the acceleration is zero because it is a constant velocity

 

[Doc Al]

the acceleration is zero because it is a constant velocity

Good. So what's F_net? And what does that tell you about F_push?

 

[bjbaldwi]

Fnet is equal to zero since the acc. is zero. F push is equal to friction force?

 

[Doc Al]

Fnet is equal to zero since the acc. is zero. F push is equal to friction force?

Exactly! You should be able to calculate the work now.

 

[bjbaldwi]

Fpush is equal to 0 and f net is equal to friction force

so Fnet=Fpush+Ffriction
Fpush=0
Fnet=Ffriction
Ffriction=Fnet =(.6)mg---->.6*13*9.8=76.44
so
Work=Fnet*D
D = 1.2m/s*8.8s---->10.56 m
so
76.44*10.56=807.2 J

 

[bjbaldwi]

Thanks for all your help : )

 

[Doc Al]

Fpush is equal to 0 and f net is equal to friction force

No, you had it right before. Fnet = 0 so Fpush = Ffriction.

so Fnet=Fpush+Ffriction
Fpush=0
Fnet=Ffriction

No, but that doesn't affect your calculation, which is correct.

It's the force Fpush that is doing the work.