The law of conservation of momentum tells us that momentum
is conserved, therefore total initial momentum should be equal to total final
momentum. In this case, we can expressed this mathematically as:
mA vA + mB vB = m v
where, m is the mass in kg, v is the velocity in m/s
since m is the total mass, m = mA + mB, we can write the
equation as:
mA vA + mB vB = (mA + mB) v
furthermore, car B was at a stop signal therefore vB = 0,
hence
mA vA + 0 = (mA + mB) v
1800 (vA) = (1800 + 1500) (7.1 m/s)
<span>vA = 13.02 m/s</span>
Haven't taken physics but I would assume if her friend is standing in front of her that you would add up the speeds and get 30 km/hr.
The force between the two objects is 19.73 nN.
<u>Explanation:
</u>
Any force acting between two objects tends to be directly proportional to the product of their masses and inversely proportional to the square of the distance between the two objects. And this kind of attraction force between two objects is termed as gravitational force.
So if we consider
and
as the masses of both objects and let d be the distance of separation of two objects. Then the force between the two objects can be determined as below:

As gravitational constant
,
= 20 kg and
= 100 kg, while d = 2.6 m, then

Thus, we get finally,

As we know, nano denoted by letter 'n' equals to 
So the force acting between two objects is 19.73 nN.
The answer is 4.0075 x 10^9