- #1

Specter

- 120

- 8

## Homework Statement

At a construction side, a small crane is raising two boxes of nails on a plank to the roof. One box has already been opened and is half full, while the other box is new. The boxes, including the nails, weight 10 kg and 20 kg, respectively, and are the same size.

Diagram:

a) If the coefficient of static friction is 0.4, draw an FBD for each box of nails and use it to calculate the angle at which each box beings to slide.

b) If the coefficient of kinetic friction is 0.3, how fast will the boxes accelerate along the plank, once they start to slide?

## Homework Equations

## The Attempt at a Solution

[/B]

a)

Box 1 = 10 kg, box 2 = 20 kg. Both FBDs are the same except for the mass of the box. For my FBD (if it's correct) should I include mgcosθ and mgsinθ?

Using the FBD:

\begin{array}{l}

μF_N=F_g \\

μF_N=mg\sinθ \\

(0.4)(mg\cosθ)=mg\sinθ \\

0.4=\frac {\sin}{\cos} \\

θ=tan^{-1}(0.4) \\

θ=21.8°

\end{array}

This is the answer for both boxes because mass and gravity cancel out in the equation, meaning that the mass of the box does not effect the angle at which each box begins to slide but the coefficient of friction does.

b) I don't know where to start for this question. I thought of using F=ma but I need to use the angle at which they begin to slide somewhere so F=ma won't work.

#### Attachments

Last edited: