Mary cycles at the speed of 6 km/h. How long will she take to reach her aunt's house which is 12 km away? How long will she take, if she cycles at the speed of 4km/h?

Half life .^87Ga is 78 h.How long will it take to decay 21% of sample of Ga?

A man sets his watch by a whistle that is 2 km away. How much will his watch be in error (speed of sound in air 330 m//s ) ?

A thief is running away on a straight road in jeep moving with a speed of 9 m s^-1 . A police man chases him on a motorcycle moving at a speed of 10 ms^-1 . If the instantaneous separation of the jeep from the motorcycle is 100 m, how long will it take for the police to catch the thief?

A 150 m long trains travelling from east to west at a speed of 20 m/s. A bird is flying from west lo cast at a speed of 5 m/s. How long will the bird take to cross the train?

An electron travelling with a speed of 5x 10^3 m/s passes through an electric field with an acceleration of 10^12 m/s^2 . How long will it take for electron to double its speed?