A man weighing 80kg is standing on a trolley weighing 320kg. The trolley resting on smooth horizontal rails. If
the man starts walking on the trolley along the rails with
a speed of 1ms", then his displacement relative to the
ground after 4 second is
1) 4.8 m 2) 4 m 3) 3.2 m 4) 2.8 m

Net displacement = 3.2 m

Explanation:

Given:

Mass of man = 80 kg

Mass of trolley = 320 kg

Speed = 1 m/s

Time = 4 sec

Computation:

Displacement by man = 1 m/s × 4 sec

Displacement by man = 4 m

Net ext force (trolley) = com at rest

So,

320 × X = 80(4 - X)

32X = 32 - 8X

40X = 32

X = 0.8 m

Net displacement = 4 m - 0.8 m

Net displacement = 3.2 m

3) 3.2 m

Explanation:

The computation of the displacement relative to the ground after 4 seconds is shown below:

Let us assume the following

Starting x coordinate is at the origin

As it does not involve any external force so x coordinated would remain unchanged

Now the separation between the man and the trolley is

= 4 m

And, we assume the displacement of man be x

So, for trolley it would be (4 -x)

Now we develop the equation which is

x = 16 - 4x

Therefore x = 3.2 m