An 80-kg man is skating northward and happens to suddenly collide with a 20-kg boy who is ice skating toward the east. immediately after the collision, the man and boy are seen to be moving together at 2.5 m/s in a direction 60° north of east. how fast was the boy moving just before the collision

The speed at which the boy was moving just before the collision is;

6.25 m/s

We are given;

Mass of man; m₁ = 80 kg

Mass of boy; m₂ = 20 kg

Initial velocity of man; u₁ = 0 m/s

Initial velocity of the boy; u₂ = ?

Speed at which the boy and the man move together after collision; v_f = 2.5 m/s

Direction of movement after collision; θ = 60° North East

    Now, in momentum when two bodies stick together after collision and move with a common velocity, the equation is represented as;

m₁u₁ + m₂u₂ = (m₁ + m₂)v

Since they move with same velocity at an angle of 60°, then;

v = 2.5cos 60

   Thus;

(80 × 0) + (20 × u₂) = (80 + 20) × 2.5 cos 60

20u₂ = 125

u₂ = 6.25 m/s

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The initial speed of the boy before the collision is 6.25 m/s.

The given parameters;

Apply the principle of conservation of linear momentum to determined the speed of the boy before the collision;

Since the boy was moving in x - direction, we will consider x - direction for the initial momentum and final momentum.

Thus, the initial speed of the boy before the collision is 6.25 m/s.

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when insulating materials rub against each other, they may become electrically charged . electrons , which are negatively charged, may be 'rubbed off' one material and on to the other. the material that gains electrons becomes negatively charged. the material that loses electrons is left with a positive charge.