Not sure if this is right but I think it’s TRUE sorry if it’s wrong....
Correct question is;
A ballet dancer spins with 2.4 rev/s with her arms outstretched,when the moment of inertia about axis of rotation is I. With her arms folded,the moment of inertia about the same axis becomes 0.6I about the same axis. Calculate the new rate of spin.
Answer:
4 rev/s
Explanation:
We are given;
Initial Angular velocity; ω_i = 2.4 rev/s
Initial moment of inertia; I_i = I
Final moment of inertia; I_f = 0.6I
From conservation of angular momentum, we have;
I_i × ω_i = I_f × ω_f
Where ω_f is the new rate of spin.
Thus, let's make it the subject to get;
ω_f = (I_i × ω_i/I_f)
Plugging in relevant values, we have;
ω_f = (I × 2.4/0.6I)
I will cancel out to give;
ω_f = 2.4/0.6
ω_f = 4 rev/s
according to conservation of momentum , in absence of external forces , the total momentum of system of the particles remain same both before and after collision.
momentum of colliding objects before collision = momentum of colliding objects after collision.
or
m1 v1i + m2 v2i = m2 v1f + m2 v2f
where m1 and m2 are the two colliding objects. v1i and v2i are their respective initial velocities before collision and v1f and v2f are their respective final velocities after collision.
hence the correct statement is
total momentum before the collision is equal to the momentum after collision.
