Question

two children of 20 kg and 25kg who are standing at the center of a skating rink. they pushed each other, second boy moved with 5m/s, then what is the velocity of the first boy?

Answer 1

$\LARGE{\bf{\underline{\underline{GIVEN:-}}}}$

• Mass of the first children (m₁) = 20 kg.
• Mass of the second children (m₂) = 25 kg.
• Initial velocity of the first boy (u₁) = 0ms⁻¹.
• Initial velocity of the second boy (u₂) = 0ms⁻¹.
• Final velocity of the second boy (v₂) = 5ms⁻¹.

$\LARGE{\bf{\underline{\underline{TO:FIND:-}}}}$

• Final velocity of the first boy (v₁)

$\LARGE{\bf{\underline{\underline{SOLUTION:-}}}}$

We can use the law of conservation of momentum:

For two or more bodies acting upon each other, their total momentum remains constant unless an external force is applied. In other words, momentum can neither be created nor destroyed.

$\to \sf{\red{m_{1}u_{1}+m_{2}u_{2}=m_{1}v_{1}+m_{2}v_{2}}}$

Substitute the values-

$\sf \to 20 \times 0 + 25 \times 0 = 20 \times v_1 + 25 \times 5$

$\sf \to 0= 20 \times v_1 + 125$

$\sf \to v_1=\dfrac{-125}{20}$

$\to \boxed{\sf{\red{ v_1=-6.25ms^{-1}}}}$

THE VELOCITY OF THE FIRST BOY - 6.25ms⁻¹.