an arrow is fired with a speed of 20.0m/s at at 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 1550m/s2 and the block's acceleration has a magnitude of 450m/s2. How long does it take for the arrow to stop moving with respect to the block? 2. Relevant equations v=vintial + acceleration(t) solve for time 3. The attempt at a solution i've used this equation but can't figure out how to get time without the positioning of the block from where the arrow was fired.