Farmers keep carbide powder in between raw mangoes. What might be the reason ? What will be the end result after 3 to 4 days ?

Make a paper tube 10 inch long and one inch in diameter. Keep once end of it on the chest of your friend on a pointer one inch to the lift side centre around 6 inches below from his/her neck. Keep your ear at the other end. Listen carefully and count the heart beats for a minute. What is the relationship between the heart beat and the pulse.

An ant moves on the floor of a room making two displacement. One of magnitude 3m and another of magnitude 4m. If the angle between the two displacements is 120^(@) what will be the magnitude of the resultant displacement ?

Some deposits were observed in water preserved in Aluminium containers after two to three days. What is the reason for the formation of these deposits?