#### pokemonlv10

##### New Member

- Joined
- Aug 22, 2016

- Messages
- 9

- Gender
- Male

- HSC
- 2017

19) The rest length of a train is 200m and the rest length of a railway platform is 160m. The train rushes past the platform so fast that , when observed in the patform's frame of reference, the train and the platform are the same length.

How fast is the train moving?

a) 0.6c -> is the answer

b) 0.75c

c) 0.8c

d) 1.25c

20) A ball is launched horizontally from a cliff with an intial velocity of u m/s. After two seconds, the ball's velocity is in the direction 45 degrees from the horizontal. What is the magnitude of the velocity in m/s at 2 seconds?

a) u

b) 1.5u

c) 19.6

d) 27.7 -> is the answer

I've tried drawing them out, rearranging formulas bt i'm just not getting the answer.