Time taken for an object to slide down a plane given μ, s and θ

[PhysicsThrow]

Homework Statement

Find the time taken for an object to slide down an inclined plane given the coefficient of friction, length of slope and angle of incline.
The coefficient of friction is 0.3.
The angle of incline is 30°.
The length of the slope is 6m.

Homework Equations

F=μN
F=(mg)sin(30)
N=(mg)cos(30)
F=ma

s=ut+1/2at²?

The Attempt at a Solution

Completely stuck. I assume I must calculate the mass of the object first? Using F=μN some how? Then I can calculate the acceleration of the object with F=ma? Then I can find the time taken to slide down with s=ut+1/2at²?

 

[Doc Al]

I assume I must calculate the mass of the object first? Using F=μN some how?

You won't need the mass. But you will need the net force. (Symbolically, not with numbers at this point.)

Then I can calculate the acceleration of the object with F=ma?

Yes, where F is the net force.

Then I can find the time taken to slide down with s=ut+1/2at²?

Yep.

 

[PhysicsThrow]

You won't need the mass. But you will need the net force. (Symbolically, not with numbers at this point.)

Ahah! I think I have it then!

ma = mg(sin(30)+-0.30cos(30)
ma = m*2.36
so, a = 2.36

 

[Doc Al]

Ahah! I think I have it then!

ma = mg(sin(30)+-0.30cos(30)
ma = m*2.36
so, a = 2.36

Good!