:uhh: First, I will state the problem - A hauling truck is traveling on a level road. The driver suddenly applies the brakes, causing the truck to decelerate by an amount (g/2). This causes a box in the rear of the truck to slide forward. If the coefficent of sliding friction between the box and the truckbed is (1/3), find the acceleration of the box relative to (a) the truck and (b) the road. Okay, here is what I have thus far - 1) part (a) will be a noninertial observer and part (b) will be an inertial observer. (So, I will have two equations) 2) The force(s) is in the horizontal direction and since it is DECELERATION, the horizontal force will be negative. 3) I am trying to solve this by starting with the sum of the forces, but I am not given a mass. I am only given friction and deceleration. I am assuming that g is gravitity. I also know the equation F=mA+ma'. Where a' is the acceleration of the object in the moving system. Could anyone give me any direction on how to pursue this problem? THANKS!!!