[填空题]
A 0.280-kg croquet bh/ c ydn9mhxg7f75xl 9all makes ani evn.a9 t 6q5ktw/*qs elastic head-on collision with a second ball initially at rest. The second ball moves off with ha*v qnwt65.qkit e9as /lf the original speed of the first ball.
(a) What is the mass of the second ball? kg
(b) What fraction of the original kinetic energy $(\Delta\mathrm{kE/KE})$ gets transferred to the second ball?