An incline plane has ф = 40.0° and μ k = 0.15. starting from rest, how long will it take a 4.0 kg block to reach a speed of 12 m/s?

     The block on the action of two forces, the Force of Friction and the Tangential Weight. Using the Newton's Secound Law, we have:


 
     Using the Velocity Hourly Equation, we get:


 
     Uniting the equations:


 
     Entering the unknowns:



Obs: Approximate results

If you notice any mistake in my english, please let me know, because i am not native.