A particle of mass m is driven by a machine that delivers a constant pow...

A particle of mass m is driven by a machine that delivers a constant power k watts. If the particle starts from rest the force on the particle at time t is

Neet 2015 | W P E Q 1 | As you can see clearly that from the year  2009, Neet is roaming around this Power concept (2010 & 2011 too had same type of qus ) so you can make your concepts crystal clear. Definitely that time aspirants were confused a lot but now you should know that  power delivered to the particle it means rate at which K.E is imparted or we can say output power .

We should know there are three types of Power. Average power , instantaneous power and net power. Here while looking at options we can understand that qus is talking about instantaneous power so we need to focus on dot product of force and velocity at that instant.

Instantaneous power is given constant so dot product of force and velocity is constant. Body is acceleration from rest so angle between force and velocity is zero because this force only is the cause of its motion. Half of its power will be used in increasing the velocity of water from 0 to V m/s and remaining half will be lost in heat , vibrations( just like charging of capacitor ). What more you can ask for. This is the benefit of attempting old qus . Now you just need to put the values in the formula.

From Newton’s second law , we know the relation between force and acceleration. Acceleration will come in terms of force and mass and later on in terms of force mass and instantaneous velocity. From equation of motion we have another relation between instantaneous velocity and acceleration so finally we will get the desired result. In a single qus we have application of W.P.E , Newton’s laws of motion and Kinematics so obviously it may not be an easy qus for many students.

 

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