Ok...Here is the problem. A block of mass 4 kilograms, which has an initial speed of 6 meters per second at time t=0, slides on a horizontal surface. (a) Calculate the work W that must be done on the block to bring it to rest. For this problem, I used the formula W= 1/2mvf ^2– 1/2mvi ^2. I solved for Work, and got an answer of -72J. I'm not sure if a negative answer is even possible for work. If the constant friction force of magnitude 8 newtons is exerted n the block by the surface, determine the following. (b) The speed v of the block as a function of the time t. To calculate the speed of the block, I used the formula V=vo + aΔt I used 6m/s as the initial velocity. 2m/s^s as my acceleration, and left t as my variable. (c) The distance x that the block slides as it comes to rest. For this part, I'm really not sure. I don't know which equation to use to solve for the distance x. How is the frictional force involved in this problem at all?