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5 years ago


Answers : (3)


total change in height = dh =H-R =50cm=0.5m

from work energy theorem,

 change in kinetic energy = total work

  kinetic energy = mgdh

 mv2(1+k2/r2)/2 = mgh

 mv2= 2mgh/(1+k2/r2)    .....................1

k is radius og gyration & for sherical ball it is Rsqrt(2/5) ...

mv2 = 10mg/7           .................2

now when theta =0 then

   N  = mv2/R

so N = 10mg/7R=10Newton

since the body is not falling off so net friction force should be equal to weight =mg

f = 0.7newton

5 years ago

thanks for the reply.... normal reaction is correct but frictional force is wrong by ur answer..... the right answer is 0.2 N 


sorry ,i forgot to tell that it is small sphere that is is rolling down the inclined plane ....


i did it this way (but failed)

frictional force = f , alpha=angular acceletion

at  point A

f - mg = ma..... (1)

f . r = I (alpha)....(2)

putting f = I (alpha)/r in (1)


for sphere I=2mr(square)/5 and alpha=a/r


2mr(sqr)/5 * a/r * 1/r=m(g+a)

2/5 a= g+a


putting this in (1)

i got f=0.46


plz remove my confusion


5 years ago

 eq 1 should be

   mg - f = ma ..........1

(this is because ,direction of net force on center of mass is downward ...)

  f = Ia/r2

mg = 7f/2

f = 2mg/7 =0.2N ans

please approve if u like my ans

5 years ago

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