A 0.15kg ball is tossed straight upward from ground level with an initial speed of 8.0m/s. Take upward as the positive y-direction and ignore air resistance.
Explain, using the sign of its momentum, how you can tell whether the ball is moving upward or downward at (i) 0.50s and (ii) 1.3s after launch. Support your answer with the appropriate numerical values of momentum.