Correct Answer is (C)
Explanation:
Let Vmg = velocity of man with respect to ground
Vtg = velocity of trolley with respect to ground
Vmt = velocity of man with respect to trolley = 1 m/s
Let M = mass of person = 80 kg
Let M' = the mass of trolley = 320kg
from relative motion
Vtg = Vmg - Vmt --------------------(1)
Initially trolley and man were at rest initial momentum = 0
According to law of conservation of momentum
VmgM + VtgM' = 0
Substituting value of Vtg from equation (1)
VmgM + (Vmg - Vmt)M' = 0
⇒ Vmg(M + M') - VmtM'
Vmg(320 + 80) = 1(320)
⇒ Vmg = 320/400 = 0.8 m/s
Thus displacement of man with respect to observer = Vmg × time = 0.8 × 4 = 3.2 m