Explanation:
Given that,
2 strings both vibrate at exactly 220 Hz. The frequency of sound wave depends on the tension in the strings.
The tension in one of them is then decreased sightly, then 
will decrese.
Beat frequency, 
So, the new frequency of the string is 217 Hz. Hence, this is the required solution.
Three forces involved in brushing your teeth are first push, then pull, then push.
The mass of a planet determines the acceleration due to gravity on it. This is according to Newton's Law of Gravitation, which basically states that the more mass a body has, the greater the force of attraction it exerts on other bodies with mass near it.
The gravitational force is:
F = GMm/r², where G is a constant, r is the distance between large mass M and small mass m.
Considering the fact that acceleration is force per unit mass, if we divide gravitational force by the small mass (to get force per unit mass), we see the dependence mathematically:
a = GM/r²
