Ski boots are usually made with releasable bindings. This is done for safety – if you fall and your ski gets caught, the binding between the boot and the ski will release so the ski pops off rather than twisting your knee. Sometimes this leads to the embarrassing situation of you falling down while skiing, the ski popping off, and the ski continuing down the mountain without you. You're skiing down a slope angled at 15∘ with respect to the horizontal when this situation happens to you. Your ski continues down the slope at a constant speed of 4 m/s. What is the coefficient of friction between your ski and the slope?