Finding velocity after a collision

Question

On a very wet and slippery rugby field a 120 kg halfback tackles a 90 kg second rower. Prior to the collision the halfback is slipping with a velocity of 5.6m/s south and the second rower is sliding with a velocity of 6.5m/s east. After the collision they move together. What is the velocity of the two players immediately after the collision?

Answer 1

its a case of conservation of momentum ( where momentum is mass x velocity and is a vector quantity)

 

Momentum of half back = 120 x 5.6 towards south

 

Momentum of second rower = 90 x 6.5 towards east

 

 Using vector components  ( where M = m₁ + m₂ = 210 kg)

MV_y = 120 x 5.6 =672 kg m/s

and MV_x = 90 x 6.5 = 585 kg m/s

 

Resultant momentum = Square root of   (672)² +( 585)² =  square root of (451584 +342225) = 891

 

Resultant velocity = 891/210 = 4.24 m/s

Using vector diagram the direction can be found. There will be loss of KE as collision is inelastic