Q.

In a scattering experiment, a particle of mass 2m collides with another particle of mass m, which is initially at rest. Assuming the collision to be perfectly elastic, the maximum angular deviation θ of the heavier particle, as shown in the figure, in radians is:                 [2025]

1 π  
2 tan-1(12)  
3 π3  
4 π6  

Ans.

(4)

Collision is perfectly elastic so both momentum and kinetic energy will be conserved.

2mv1=2mv1fcosθ+2mv2fcosϕ                      ...(i)

2mv1fsinθ=mv1fsinϕ                                           ...(ii)

12(2m)v12+12m(0)2=12(2m)v1f2+12mv2f2

2v12=2v1f2+v2f2                   ...(iii)

From eq. (i), (ii) and (iii),

3v1f2-4v1v1fcosθ+v12=0

(-4v1cosθ)2-4(3)(v12)0

cos2θ34  or,  cosθ32

 θ=π6