A pebble is thrown vertically upwards from a bridge with an initial velocity of 4.9 m/s. It strikes the water after 2s. If acceleration due to gravity is `9.8 m//s^(2)(a)` what is the height of the bridge? (b) with what velocity does that pebble strike the water?

Answer

B

Explanation

Time taken from from point P to point P `" " T_(P)=2sqrt((2(h+H))/g)`
Time taken from point Q to point Q `" "T_(Q)=2sqrt((2h)/g)`
`rArr T_(P)^(2)=(8(h+H))/g` and `T_(Q)^(2)=(8h)/g rArr T_(P)^(2)=T_(Q)^(2)+(8H)/g rArr g=(8H)/(T_(P)^(2)-T_(Q)^(2))`