two boys paul mass 60kg and john mass 40kg are standing on skateboards. They place their hands against each other and push away from each other so that they start to move in opposite direction. (a) if paul moves to the left with velocity of 0.8m/s.. Calculate john's velocity

The law of conservation of linear momentum

0 =- m1•v1 + m2•v2
v2 = m1•v1/m2 =60•0.8/40=1.2 m/s

To calculate John's velocity, we can use the principle of conservation of momentum. According to this principle, the total momentum before pushing away from each other should be equal to the total momentum after pushing away from each other.

Let's denote Paul's velocity as v₁, John's velocity as v₂ (the direction positive for both boys is to the right), and the mass of Paul as m₁ (60 kg) and the mass of John as m₂ (40 kg).

We can express the principle of conservation of momentum as:

(m₁ * v₁) + (m₂ * v₂) = 0

Since Paul moves to the left with a velocity of 0.8 m/s, we can substitute the values:

(60 kg * -0.8 m/s) + (40 kg * v₂) = 0

Now, let's solve for v₂:

(-48 kg·m/s) + (40 kg * v₂) = 0

40 kg * v₂ = 48 kg·m/s

v₂ = (48 kg·m/s) / 40 kg

v₂ = 1.2 m/s

Therefore, John's velocity is 1.2 m/s to the right.