What is the magnitude of impulse of a 2.7 gram ping pong ball , initially at 15m/s , if hit by a ping pong paddle and then moves in the opposite direction at 14 m/s ?

Three archers each fire four arrows at a target. joe’s four arrows hit at points 10 cm above, 10 cm below, 10 cm to the left, and 10 cm to the right of the center of the target. all four of moe’s arrows hit within 1 cm of a point 20 cm from the center, and flo’s four arrows hit within 1 cm of the center. the contest judge says that one of the archers is precise but not accurate, another archer is accurate but not precise, and the third archer is both accurate and precise. which description applies to which archer? explain

Could someone . i have tried to solve myself but my calculation is off

Why is it important always to use horizontal bars in unit fractions when performing unit conversions?