(a) If a train traveling at `72 km//h` is to be brought to rest in a distance of `200 m`, find the deceleration.
(b) The velocity of a bullet is reduced from `200 m//s` to `100 m//s` while traveling through a wooden block of thickness `10 cm`. Find the retardation (assuming it ti be uniform).

Explanation

(a) `u=72 km//h=72xx5/18=20 m//s, v=0,s=200m`
`v^(2)=u^(2)+2as`
`0=(20)^(2)+2axx100impliesa=-2 m//s^(2)`
i.e. deceleration `=2m//s^(2)`
(b) `u=200 m//s, v=100 m//s, s=10 cm=0.1m`
`v^(2)=u^(2)-2as`
`impliesa=((200)^(2)-(100)^(2))/(2xx0.1)=(300xx100)/0.2`
`=15xx10^(4) m//s^(2)`