This was on a test of mine and I can't really figure out how to do it. I was going to relate the final total kinetic energy of the system and then subtract the new (stuck) mass to find the total energy loss. That is the only way i can think of to approach the problem, could someone explain how to do it?
(Problem) Two football players collide and stick together. One has a mass of 75 kg and is moving to the right at 5 m/s, while the other has a mass of 120 kg and is moving to the left at 1 m/s. Find the total loss of kinetic energy in joules.
Please help... I'd really like to figure out how to do this one. thanks
(Problem) Two football players collide and stick together. One has a mass of 75 kg and is moving to the right at 5 m/s, while the other has a mass of 120 kg and is moving to the left at 1 m/s. Find the total loss of kinetic energy in joules.
Please help... I'd really like to figure out how to do this one. thanks
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KE lost = total initial KE of both - final joint KE
The joint velocity (v) is required after collision .. use conservation of momentum (which applies to any kind of collision.)
As momentum is a vector quantity directions must be taken into account ..
Assuming motion to the right is +ve
Total mom before = joint mom afterwards
(75kg x 5.0m/s→) - (120kg x 1.0m/s←) = (75+120)kg x v
255 = 195v .. .. v = 1.31 m/s
Final KE = ½ (75+120) (1.31)² = 167.30 J
Initial KE = (½ x 75 x 5²) + (½ x 120 x 1.0²) = 997.50 J
KE loss = 997.50 - 167.30 .. .. ►KE loss = 830.20 J
The joint velocity (v) is required after collision .. use conservation of momentum (which applies to any kind of collision.)
As momentum is a vector quantity directions must be taken into account ..
Assuming motion to the right is +ve
Total mom before = joint mom afterwards
(75kg x 5.0m/s→) - (120kg x 1.0m/s←) = (75+120)kg x v
255 = 195v .. .. v = 1.31 m/s
Final KE = ½ (75+120) (1.31)² = 167.30 J
Initial KE = (½ x 75 x 5²) + (½ x 120 x 1.0²) = 997.50 J
KE loss = 997.50 - 167.30 .. .. ►KE loss = 830.20 J