A boy standing idle sounds a whistle to his friend at a distance of 1200 m moving away from him in a speeding car at 108 kms /hr. Find the duration after which his friend is going to hear him. (Speed of sound = 330m/sec). Pick.
A) 3.6 secs B) 4.00 secs C) 40 secs D) 45 secs E) None of these
If friend hears sound after t secs, then   330*t = 1200 +(108*5/18)*t   300t =1200   t= 4 secs   ANSWER:4.00 secs
<result>B</result>
A boy standing idle sounds a whistle to his friend at a distance of 1200 m moving away from him in a speeding car at 108 kms /hr. Find the duration after which his friend is going to hear him. (Speed of sound = 330m/sec).