At one instant, the center of mass of a system of two particles is located on the x-axis at 2.0 cm and has a velocity of (5.0 m/s) ˆx. One of the particles is at the origin. The other particle has a mass of 0.10 kg and is at rest on the x-axis at x = 8.0 m. a) What is the mass of the particle at the origin? b) Calculate the total momentum of this system. c) What is the velocity of the particle at the origin?

Given that,

At one instant,

Center of mass is at 2m

Xcm = 2m

And velocity = 5•i m/s

One of the particle is at the origin

M1=? X1 = 0

The other has a mass M2=0.1kg

And it is at rest at position X2 = 8m

a. Center of mass is given as

Xcm = (M1•X1 + M2•X2) / (M1+M2)

2 = (M1*0 + 0.1*8) / (M1 + 0.1)

2 = (0 + 0.8) / (M1 + 0.1)

Cross multiply

2 (M1+0.1) = 0.8

2M1 + 0.2 = 0.8

2M1 = 0.8-0.2

2M1 = 0.6

M1 = 0.6/2

M1 = 0.3kg

b. Total momentum, this is an inelastic collision and it momentum after collision is given as

P = (M1+M2) V

P = (0.3+0.1) * 5•i

P = 0.4 * 5•i

P = 2 •i kgm/s

c. Velocity of particle at origin

Using conversation of momentum

Momentum before collision is equal to momentum after collision

P (before) = M1 • V1 + M2 • V2

We are told that M2 is initially at rest, then, V2=0

So, P (before) = 0.3V1

We already got P (after) = 2 •i kgm/s in part b of the question

Then,

P (before) = P (after)

0.3V1 = 2 •i

V1 = 2/0.3 •i

V1 = 6 ⅔ •i m/s

V1 = 6.667 •i m/s