Question

Question 6.16 Two identical ball bearings in contact with each other and resting on a frictionless table are hit head-on by another ball bearing of the same mass moving initially with a speed V. If the collision is elastic, which of the following figure is a possible result after collision?

Chapter Work, Energy And Power Page 136

Answer 1

Hi---------

we know that
in elastic collision , the initial and final kinetic energy is same
so
case 1, case 3
it have no elastic collision ,hence it kinetic energy is not conserved
case2
it have elastic collision ,hence kinetic energy is conserved .
hope it help u

Answer 2

Tw balls are identical , Let each ball of mass = m
initial speed of two balls resting on frictionless table is 0 and another ball is v

before collision :
kinetic energy = 1/2m(0)² + 1/2m(0)² + 1/2mv²
= 1/2mv²

because collision is elastic head on collision so kinetics energy must be conserved . e.g kinetic energy before collision = kinetic energy after collision .

check each of the following case
______________________________
(a) kinetic energy after collision = 1/2m(0)² + 1/2m(v/2)² + 1/2m(v/2)²
= 0 + mv²/8 + mv²/8
= mv²/4
kinetic energy before collision ≠ kinetic energy after collision . so, (a) is wrong

(b) kinetic energy after collision = 1/2m(0)² + 1/2m(0)² + 1/2m(v)²
= 1/2mv²
here,
kinetic energy before Collision= kinetic energy after collision .
hence, option (B) is correct .

(c) kinetic energy after collision = 1/2m(v/3)² + 1/2m(v/3)² + 1/2m(v/3)²
= 3 × 1/2mv²/9
= mv²/6
kinetic energy before collision ≠ kinetic energy after collision.
hence (c) is wrong .


hence, only option (B) is correct or suitable .