Kinematics Question 330
Question: A 120 m long train is moving towards west with a speed of 10 m/s. A bird flying towards east with a speed of 5 m/s crosses the train. The time taken by the bird to cross the train will be [Manipal 2002]
Options:
A) 2h
B) 2h 40 min
C) 1h 20 min
D) Cannot be estimated with the information given
Correct Answer: B Boat covers distance of 16km in a still water in 2 hours. i.e. $ v _{B}=\frac{16}{2}=8km/hr $ N ow velocity of water Time taken for going upstream $ t_1=\frac{8}{v _{B}-v _{w}} $ $ =\frac{8}{8-4}=2hr $ (As water current oppose the motion of boat) Time taken for going down stream $ t_2=\frac{8}{v _{B}+v _{w}} $ $ =\frac{8}{8+4}=\frac{8}{12}hr $ (As water current helps the motion of boat) $ \therefore $ Total time $ =t_1+t_2=( 2+\frac{8}{12} )hr $ or 2hr 40minShow Answer
Answer:
Solution:
$ \Rightarrow v _{w}=4km/hr $ .
