Classes
Class 9Class 10First YearSecond Year
$An electron \left(\mathrm{m}=9.1 \times 10^{-31} \mathrm{~kg}\right) traveling at 2.0 \times 10^{7} \mathrm{~ms}^{-1} undergoes a head on collision with a hydrogen atom \left(\mathrm{m}=1.67 \times 10^{-27} \mathrm{~kg}\right) which is initially at rest. Assuming the collision to be perfectly elastic and a motion to be along a straight line find the velocity of hydrogen atom?$

$A boy places a fire cracker of negligible mass in an empty can of 40 \mathrm{~g} mass. He plugs the end with a wooden block of mass 200 \mathrm{~g} . After igniting the firecracker he throws the can straight up. It explodes at the top of its path. If the block shoots out with a speed of 3 \mathrm{~ms}^{-1} how fast will the can be going?$

$Explain the circumstances in which the velocity " v " and acceleration "a" of a car are:(iv) " v " " is zero but "a" is not$

$Explain the circumstances in which the velocity " v " and acceleration "a" of a car are:(v) "a" is zero but " v " is not zero$

$A hose pipe ejects water at a speed of 0.3 \mathrm{~ms}^{-1} through a hole of area 50 \mathrm{~cm}^{2} . If the water strikes a wall normally calculate the force on the wall assuming the velocity of the water normal to the wall is zero after striking.$

$Each of the following questions is followed by four answers one of which is correct answer. Identified that answer.(i) What is meant by a ballistic trajectory?(a) The paths followed by an un-powered and unguided projectile is called ballistic trajectory.(b) The path followed by the powered and unguided projectile is called ballistic trajectory.(c) The path followed by un-powered but guided projectile.(d) The path followed by powered and guided projectile.$

$A 1500 kg car has its velocity reduced from 20 \mathrm{~ms}^{-1} to 15 \mathrm{~ms}^{-1} in 3 . S . How large was the average retarding force.$