Negative sign indicates that the direction in which the pistol would recoil is opposite to that of bullet.
Two bodies as shown in the figure collide with each other and join thereafter. With what velocity will they move after combining together?
m1 = 60 kg
u1 = + 5 m/s positive direction
v = ?
m2 = 55 kg
u2 = -6m/s negative direction
v = ?
Total momentum of two bodies before collision
= m1u1 + m2u2
= 60 x 5 + 55 x -6
= -30 kg m/s
If v is the velocity of two joined bodies. After collision, the total momentum will be
= m1v1 + m2v2 (v1 = v2)
= (m1 + m2)v
= (60 + 55) kg x v m/s
= 115 v
∴ According to law of conservation of momentum
= m1u1 + m2u2 = m1v1 + m2v2
= -30 kg m/s = 115 v
∴ v = -30/115 = -0.26 m/s
∴ Two bodies will move with velocity 0.26 m/s in the direction of the second body.