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Question

A solid sphere of radius r=2 m is under a combination of rotational and translational motion as shown in figure.


If acceleration of COM (O) is ao=2 m/s2 and acceleration of point A is aA=6 m/s2, then find angular acceleration α.

A
4 rad/s2
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B
6 rad/s2
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C
2 rad/s2
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D
1 rad/s2
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Solution

The correct option is C 2 rad/s2
Given:
aA=6 m/s2; a0=2 m/s2
As we know that,
aA=aCOM+(α×rOA)
aA=a0+(α×rOA)
aAa0=α×rOA ....(i)
Here,
aA=6^i m/s2
a0=2^i m/s2
α×rOA=(α^k)×(2^j)
α being the magnitude of angular acceleration.
α×rOA=2α(^k×^j)=+2α^i rad/s2
On substituting in Eq.(i) we get,
6^i2^i=2α^i
On equating the coefficients of ^i both sides:
4=2α
Or, α=2 rad/s2
option (c) is correct.

Alternate solution:
We know that acceleration of top most point in rolling motion is
aA=a0+rα
The tangential acceleration (rα) of point A and acceleration of centre of mass(a0), both are along the same direction (i.e +ve x direction).
6=2+2α
α=2 rad/s2

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