1can u giv an example which is more earthly?!? :P
Q1 > A particle of mass 'm' is moving in a circular path of constant radius 'r' such that its centripetal acceleration 'a' is varying with time as a=k*k*r*t*t, where 'k' is a constant. Find the power delivered to the particle by the force acting on it.
Q2 > Can the kinetic energy of a body increase without the application of external force? Explain with 2 examples.
Q3 > A body of mass 'm1', standing on a smooth horizontal plane of ice throws a ball of mass 'm2' [m2 does not mean 2*m.It is a separate mass without any relation to 'm1'] horizontally on the surface of ice. If they be at a distance 'x' from each other after time 't', show that the amount of work done by the boy in throwing the ball is:
(1/2)*(x/t)*(x/t)*{(m1*m2)/(m1+m2)}
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15 Answers
492) Yes... suppose a system crumbling down by the action of it's own gravity!! (if you know abt black holes u know what I am talking abt)
12nd qstn: this is a weird example i`m giving....i may not be right....
but when we move our hands with some velocity,its kinetic energy is changing,where is the ext. force??
1is the first answer ' m k4r2t5/3 ' ?
a = dv/dt
=> on integrating instantaneous velocity at some time t = k2rt3/3
.:. power = F.v = mav = m * k2rt2 * k2rt3/3 = m k4r2t5/3
1for the last one,
conserve momentum = >m1v1 = m2v2
and x = v1t + v2t
change in kinetic energy of the system after time t,
= (1/2)*(x/t)*(x/t)*{(m1*m2)/(m1+m2)}
1hey debosmit! if u r rubbing ur hands then akording to u there is friction btwn the handz n dat iz da increase in kinetic energy...ryt? but there is an external force akting in this case- the force due to mechanical movement of the hands..widout movng the hands how will the friction arise? so...buddy..i dnt think thatz a correct answer..
1yes rishabh...it seems ur ryt...bt cud u pls elaborate on ur answers a bit..it wud b easier fr me to undrstnd..
262what about an explosion ? only internal force cause the increase in kinetic energy.
1yep!! datz da right answer aditya!!! any kind of explosion which is not initiated by any external force...
1how will friction arise if u just move ur hands....i`m not giving the case of rubbing....
1oh...so u mean the kinetic energy of the hands increases?
but there also ur applying an external force,i.e., the force applied by ur hands in order to make them move. Im askin fr a condition wen there is increase in kinetic energy widout ne xtrnal force...will the kinetic energy of ur arms increase if u simply keep them still widout moving?? NO..
49arey yaar....
replace the word body by the word system..
then consider each body to be a "system" of infinite particles...
Your life becomes easy thus.
49suppose earth moon system is the only thing present in universe and they are not revolving...
Thus they wud fall into one another...
And as they approach, their KE would increase @ the cost of PE..
U can do same logicing for 2 molecules...