Q₁- Two particles 1 and 2 move with constant velocities v₁ and v₂. At the initial moment, their radius vectors are r₁ and r₂. How must these four vectors be interrelated for the particles to collide? 

Q₂- A ship moving along the equator to the east with velocity v₀ = 30 km/hr. The south-eastern wind blows at an angle φ =60⁰ to the equator with velocity v = 15 km/hr. Find the wind velocity v’ relative to the ship and the angle φ’ between the equator and the wind direction in the reference frame fixed to the to the ship.

Solution: