When Does the Box Start to Slip on the Ramp?

[Chandasouk]

Homework Statement

A box of textbooks of mass 26.0 kg rests on a loading ramp that makes an angle \alpha with the horizontal. The coefficient of kinetic friction is 0.240 and the coefficient of static friction is 0.360.

As the angle \alpha is increased, find the minimum angle at which the box starts to slip.

At this angle, find the acceleration once the box has begun to move.
Take the free fall acceleration to be g = 9.80 m/s^2.

At this angle, how fast will the box be moving after it has slid a distance 4.60 m along the loading ramp?
Take the free fall acceleration to be g = 9.80 m/s^2.


For the first part I got

$$\mu$$k = tan$$\theta$$

0.360 = tan$$\theta$$

But how do I evaluate this on my calculator? When I put in arctan(.360) I get a decimal for a degree and same if i input it as tan(.360)

 

[whs]

You say you get a decimal? Is that bad? Were you expecting a nice whole number?

Or do you mean you need your calculator to be in radians rather than degrees?

 

[SuperCass]

I have a VERY similar problem like this one. How did you get tan$$\theta$$ to equal $$\mu$$k ?

 

[Redbelly98]

You need to:

1. Use the arctan function on your calculator, sometimes also called atan or tan^-1
2. Make sure the calculator is in the correct angle mode, radians or degrees.

 

[SuperCass]

No I mean how do you know it equals that?

 

[Redbelly98]

Solving this problem starts with drawing a free body diagram , showing all the forces acting on the mass. Have you done that?