An arrow is fired with a speed of 20.0 m/s at a block of Styrofoam resting on a smooth surface. The arrow penetrates a certain distance into the block before coming to rest relative to it. During this process the arrow's deceleration has a magnitude of 1550 m/s^2 and the block's acceleration has a magnitude of 450 m/s^2. a) how long does it take for the arrow to stop moving with respect to the block? b) what is the common speed of the arrow and the block when this happens? c) how far into the block does the arrow penetrate?