86.As a man moves directly away from a steady source of sound at constant speed, the sounds he hears will :

87.If a body starts its motion from a point and comes back to its initial position after a certain time then since :

88.It takes much longer to cook things in the hills than in the plains, because :

89.Usually light travels faster than sound. However, when we switch a television set on the picture comes later than the sound. The reason is that :

90.Air-pockets that cause aircrafts to lose altitude sudenly are caused by :