What is the speed of the vehicle and truck together after crash?

Question

A 1920 kg vehicle going with a speed of 27 m/s collides with the back of 2490 kg truck. The vehicles lock guards.

a) What is the speed of the vehicle and truck together after crash? (accepting 100% of energy stays as KE)

b) What is the Kinetic Energy of the system before the crash? What about after the collision?

c)Is the collision elastic or inelastic?

Answer 1

A 1920 kg vehicle going with a speed of 27 m/s collides with the back of 2490 kg truck. The vehicles lock guards.

a) What is the speed of the vehicle and truck together after crash? (accepting 100% of energy stays as KE)

b) What is the Kinetic Energy of the system before the crash? What about after the collision?

c)Is the collision elastic or inelastic?

Part c) first

the collision is inelastic as after collision body are locked together

Part a)

Using momentum conservation

2490* 27 + 2490*0 = ( 1920 + 2490 ) V

where V = speed of two locked together

V = 57230/4410 m/s

KE before crash = 1/2 (1920)( 27)² J (As KE of other body is zero assuming it to be at rest before collision)