Question

Two balls A and B having masses 1kg and 2kg, moving with speed 21 m/s and 4 m/s respectively in opposite direction, collide head on. After collision A moves with the speed of 1 m/s in the same direction, then correct statement is :

• A. The velocity of B after collision is 6m/s opposite to the direction of motion before collision
• B. The coefficient of restitution is 0.2
• C. The loss of kinetic energy due to collision is 200 J
• D. The impulse of the force between two balls is 40 Ns

Answer 1

Answer: (A), (B), (C)

The correct options are
A The velocity of B after collision is 6m/s opposite to the direction of motion before collision
B The coefficient of restitution is 0.2
C The loss of kinetic energy due to collision is 200 J

Law of con. of momentum.
$m_1{v}_1+m_2{v}_2=m_1{v}_3+m_2{v}_4$
$1\times 21+2\times (-4)=1\times 1+2vv=6m/s$
i.e, direction of B is reversed.
$e=\frac{vel.ofseparation}{vel.ofapproach}=\frac{6-1}{21-(-4)}=0.2$

loss in K.E.$=\frac{1}{2}(1\times 21\times 21+2\times 4\times 4-1\times 1\times 1-2\times 6\times 6)=200J$

impulse $=2\times 6-2\times (-4)=20Ns$