Question

**7.** [1pt]

A boxcar of length 8.00 m and height

2.40 m is at rest on frictionless rails. The empty boxcar has a
mass of 2800 kg. Inside the boxcar, located at the

left end, is a tank containing 2550 kg of water. The tank is 1.90 m
long and 2.40 m tall. The tank starts to leak, and the water fills
the floor of the boxcar uniformly. Assume that all the water stays
in the box car. After all the water has leaked out of the tank,

a) what will be the final velocity of the boxcar? (Take movement to the right as positive.)

b) What is the displacement of the boxcar 7 s after the water has settled in the bottom? (Take positive displacement as being to the right.)

Answer #1

Therefore by conservation of momentum

Final momentum = Initial momentum

Final momnetum = 0

Hence the final velocity = 0

(b) Initial cente of mass of the system

X_{Cm} = (m_{1}X_{1} +
m_{2}X_{2} )/(m_{1} +m_{2})

X_{cm} = (2800*4 + 2550*0.95)/(2800+2550) = 2.546 m

Now after water settle down then the new center of mass will be
x_{cm} = 8/2 = 4 m

Now the displacement will be = X_{cm} - x_{cm} =
2.546 - 4 = - 1.454 m

-ve sign means displacement should be toward left.

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