Q18 / 122 · NTA Abhyas (JEE Main) 2020 · Physics · Rotational Motion

A small ball of mass m and radius r=R10 rolls without slipping along the track shown in the figure. The radius of circular part of the track is R. If the ball starts from rest at a height of 8R above the bottom, the normal force on the ball at the point P is

Figure

  • A
    1003mg
  • Correct answer
    B
    1009mg
  • C
    2009mg
  • D
    507mg

Solution

Using Work-Energy Theorem

7mgR=12mv2+1225mr2×ω2

since the sphere is rolling without slipping  v=rω

∴7mgR=12× 75mr2× v2r2

⇒v2=10gR

at point P, we can consider sphere as a point object doing circular motion in a circle of the radius (R-r) with velocity v,

Hence at point P

N=mv2R-r=10mgRR-R10=10mgR9R10   ( given r=R10 )

or N=1009mg

Hence, the correct answer is option: 'B'.

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