# Class 9 Physics Dynamics

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$A thermos flask containing milk as a system is shaken rapidly. Does the temperature of milk rise?$

$Show that ratio of the root mean square speeds of molecules of two different gases at a certain temperature is equal to the square root of the inverse ratio of their masses.$

$3.5 A body has weight 20 \mathrm{~N} . How much force is required to move it vertically upward with an acceleration of 2 \mathrm{~ms}^{-2} ? (24 N)$

$ii. Inertia depends upon(a) force(b) net force(c) mass(d) velocity$

$A heat engine performs 100 \mathrm{~J} of work and at the same time rejects 400 \mathrm{~J} of heat energy to the cold reservoirs. What is the efficiency of the engine?$

$3.2 The weight of a body is 147 \mathrm{~N} . What is its mass? (Take the value of g as 10 \mathrm{~ms}^{-2} )(14.7kg)$