Question

A ball$A$ is moving with velocity $5m/s$ collides elastically with another identical ball $B$ which is initially at rest such that the velocity of $B$ after the collision makes an angle of ${37}^{\circ }$ with the initial velocity of $A$. Then the INCORRECT statement is :

• A. Speed of$A$ after collision is $3m/s$
• B. Speed of$B$ after collision is $4m/s$
• C. Balls $A$ and $B$ move at right angle after collision
• D. Kinetic energy is not conserved as the collision is not head on.

Answer 1

The correct option is B Speed of$B$ after collision is $4m/s$

According to conservation of momentum,in the direction perpendicular to initial velocity

$m{v}_1\sin 60=m{v}_2\sin 60$

$v_1=v_2$

again conservation of linear momentum according to the initial velocity,

$mu=m{v}_1\cos 30+m{v}_2\cos 30$

$5=2v_2\frac{\sqrt{3}}{2}$

$v_2=\frac{5}{\sqrt{3}}$

Thus velocity of ball B after collision $=\frac{5}{\sqrt{3}}$