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Class 9Class 10First YearSecond Year
$An amoeba of mass 1.0 \times 10^{-12} \mathrm{~kg} propels itself through water by blowing a jet of water through a tiny orifice. The amoeba ejects water with a speed of 1.0 \times 10^{-4} \mathrm{~ms}^{-1} and at a rate of 1.0 \times 10^{-13} \mathrm{kgs}^{-1} . Assume that the water is being continuously replenished so that the mass of the amoeba remains the same.(a) If there were no force on amoeba other than the reaction force caused by the emerging jet what would be the acceleration of the amoeba?(b) If amoeba moves with constant velocity through water what is force of surrounding water (exclusively of jet) on the amoeba?$

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

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

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

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

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

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