- #1

amal

- 28

- 0

## Homework Statement

https://mail-attachment.googleusercontent.com/attachment/u/0/?ui=2&ik=b1f5382d97&view=att&th=141a110b2b42e985&attid=0.1&disp=inline&realattid=1448488861572371361-local0&safe=1&zw&saduie=AG9B_P_C76QVFT1TasjVUas0veFX&sadet=1381397823049&sads=-V90GcdzfB5o4PRtBTmYd5KF_q0&sadssc=1

The coefficient of static friction [itex]μ_s[/itex] between the 100kg block and wedge is [itex]0.20[/itex]. Determine the magnitude of force [itex]P[/itex] required to raise the block if the rollers are frictionless and wedge massless. You may take [itex]g=9.8m/s^2[/itex]

## Homework Equations

[itex]f=μ_s*N[/itex]

## The Attempt at a Solution

https://mail-attachment.googleusercontent.com/attachment/u/0/?ui=2&ik=b1f5382d97&view=att&th=141a110b2b42e985&attid=0.2&disp=inline&realattid=1448488861572371361-local1&safe=1&zw&saduie=AG9B_P_C76QVFT1TasjVUas0veFX&sadet=1381397837108&sads=2EHbpPS-gjUWKviSaADc7HNu_Rc

The block will move whenever there is relative motion between block and wedge.

Now,

[itex]N_1+Psinθ=Wcosθ[/itex]

[itex]N_1=Wcosθ-Psinθ[/itex]

[itex]f=μ_sN_1[/itex]

For impending motion,

[itex]f=Psinθ[/itex]

That will give:

[itex]P={\frac{Wμcosθ}{cosθ+μsinθ}}[/itex]

Plugging in the values,

[itex]P=186.03N[/itex]

Only that my teacher thinks that the answer is wrong. According to him, P should be 465N and N1 should be 1073N odd. Though he didn't elaborate, he thinks that something is wrong with my resolution of P. I don't understand how and I also don't understand why the normal is greater than the weight of the block.

Please Help.