Question

Erica (38 kg ) and danny (43 kg ) are bouncing on a trampoline. just as erica reaches the high point of her bounce, danny is moving upward past her at 4.7 m/s . at that instant he grabs hold of her.part awhat is their speed just after he grabs her?

Answer 1

2.5 m/s going upward.
   In the situation described, Erica and Danny undergo a non-elastic collision which will conserve their combined momentum. Since Erica is stationary, her momentum is 0. And since Danny is moving upward at 4.7 m/s his momentum is 43 kg * 4.7 m/s = 202.1 kg*m/s. Assuming that both Erica and Danny will be moving as a joined system, their combined mass is 38 kg + 43 kg = 81 kg. Since the momentum will be the same, their velocity will be 202.1 kg*m/s / 81 kg = 2.495061728 m/s. Since we only have 2 significant figures in the provided data, rounding the result to 2 significant figures gives a velocity of 2.5 m/s going upward.