physic 難題 一

Q7. option D
since potential energy is propotional to height.

Q9. Use conservation of momentum
momentum of train = 8x10^4 x 10/3.6 kg-m/s = 222000 kg.m/s
hence, 222000 = 100v
where v is the speed of ejection of water
i.e. v = 2220 m/s

The answer is option G