Can anyone help me with a physics question???

Question

2 blocks of masses 1kg & 18kg are placed on a horizontal, frictionless surface. A light spring is attached to one of them, & the blocks are pushed together with the spring between them. A cord holding them together is burned, after which the block of mass 18kg moves to the right with a speed of 4.8m/s. What is the velocity of the other mass?

Is this an elastic collision? The spring between the cars sort of confuses me..I'm not sure what formula to use..anyone know?

Answer 1

After reading that....."MY HEAD HURTS".........lol

Answer 2

The momentum on each block should be the same but in opposite direction.

M1V1 = -M2V2

18*4.8 = -1*V2

V2 = -86.4 m/s

Yes, it should be elastic since they are on frictionless surface (ie no external force)

Think of one block has a spring attached to it, the other has none. The spring is compressed and then released. The blocks will then be forced apart by the spring in opposite direction.

Answer 3

The law of conservation of linear momentum is correct.

Answer 4

The 1 kg mass will move with speed 4.8 x -18 m/s = -86.4 m/s so that the total momentum m1v1 + m2v2 of the system can remain zero.

Technically speaking it is an elastic collision because energy is conserved. The spring simply serves to propel the two bodies (blocks or cars) apart. Its initial compressional potential energy is converted into the kinetic energy of the blocks.