Is my physics quiz on confirmations correct?

[CanadianEh]

Hi there, I have a multiple choice quiz that I completed for my physics class and I'm looking for confirmation on whether I'm correct or not.

1.The centre of mass of an object...
A. Must always lie outside the object, at a point where there is no mass.
B. May lie outside the object, at a point where no mass is.
C. Must always lie within the mass of the object



2. Consider a ball on the end of a string being whirled in a horizontal circle. The horizontal force acting on the ball points...
A. outwards, away from the centre of the circle
B. inwards, towards the centre of the circle
C. ... nonsense. There is no force at all on the ball



3. A man is standing on a turntable holding a dumbell in each of his outstretched hands. He is rotating at 1 rev/s. If he now brings his hands in close to his chest,
A. his rotational speed decreases
B. his rotational speed is unchanged
C. his rotational speed increases

The answers I got are B, B and C respectively. Can anyone confirm?

 

[PhanthomJay]

looks good!

 

[kerimek]

I can confirm that your answers are correct. The centre of mass of an object can lie outside the object, but it must always be within the mass of the object. In the case of the ball on a string, the horizontal force acting on the ball points inwards towards the centre of the circle, and when the man on the turntable brings his hands in, his rotational speed increases due to the conservation of angular momentum. Good job on your quiz!