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## Homework Statement

A 4.0-kg toboggan rests on a frictionless icy surface, and a 2.0 kg block rests on top of the

toboggan. The coefficient of static friction µs between the block and the surface of the toboggan is 0.60, whereas the kinetic friction coefficient is 0.51. The block is pulled by a

30 N horizontal force as shown. What are the magnitudes and directions of the

resulting accelerations of the block and the toboggan?

## Homework Equations

F

_{fr}= [tex]\mu[/tex]s Fn = [tex]\mu[/tex]s mg

F

_{fr}= [tex]\mu[/tex]k Fn = [tex]\mu[/tex]k mg

Fn = mg

[tex]\Sigma[/tex]F= ma

## The Attempt at a Solution

Fn= (m1 + m2) g

Fn= (2.0kg + 4.0kg) (9.80m/s2)

Fn= 58.8 N

Now I calculate the friction of both separately: (im not sure about this part)

Box:

Ffr = 0.60 (58.8N)

Ffr = 35.25N

Tob:

Ffr = 0.51 (58.8N)

Ffr= 29.988N

Then I attempt the acceleration:

[tex]\Sigma[/tex]=m1a

Fr-F=ma

35.25N-30N = (2kg) a

5.25N/2kg = a

2.625 m/s2 = a

[tex]\Sigma[/tex]= m2a

F-Ffr =ma

30N-29.988N = (4kg) a

0.003 m/s2 = a (or 3 x 10

^{-3})

This is where I get confuse. When the box is pulled doesn't it stay static while the sled slides on the ice? And what do they mean by direction?

Any help would be great :)