Hello, I have a question for homework. The question reads: A body of mass m=4.8 kg is standing on a ramp inclined in an angle of α=12 degrees. The static friction coeficient between the ramp and the body is μ=0.24. The ramp, which is inclined to the left, is in a train, which accelerates to the right. What is the minimal acceleration of the train that will cause the body to slide up the ramp? I thought that for the box to slide up force greater than Ff+4.8*9.8*sin(12) should be applied by train (..by friction that is). From there acceleration of train with respect to the box can be calculated. However I unable to figure out how calculate the acceleration with respect to earth. Would appreciate any advice.