The bar in Problem 46 has mass m and is initially at rest. A constant force F(vector) ?to the right is applied to the bar. Formulate Newton?s second law for the bar, and find its velocity as a function of time.

Data From Problem 46

Figure 27.39 shows a pair of parallel conducting rails a distance l apart in a uniform magnetic field B(vector). A resistor R is connected across the rails, and a conducting bar of negligible resistance is being pulled along the rails with velocity v ! to the right. (a) What direction is the current in the resistor? (b) At what rate does the agent pulling the bar do work???

_ x x x X x x X .R FIGURE 27.39 Problems 46-49 and 75