An indestructible bullet 2.00cm long is fired straight through a board that is 10.0cm thick. The bullet strikes the board with a speed of 420 m/s and emerges with a speed of 280m/s. (a) What is the average acceleration of the bullet through the board? (b) What is the total time that the bullet is in contact with the board? (c) What thickness of board (calculated to 0.1cm) would it take to stop the bullet, assuming that the acceleration through all boards is the same? We can use these equasions (v0=initial velocity, D=displacement): v = v0 + at D = v0t + (1/2)at2 v2 = v02 + 2aD D = (1/2)(V0+V)t D = vt - (1/2)at2 I have found that the answer to part (a) is equal to -490,000m/s2, but I cannot figure out how to do parts (b) and (c). Please help?!