Q

# Try this! An open box-car has a mass of 30,000 kg and is moving on a level railroad track at 4.00 m/s. 1,000 kg of water falls straight down into the box-car. The velocity of the box-car after the water falls into the box-car is

An open box-car has a mass of 30,000 kg and is moving on a level railroad track at 4.00 m/s. 1,000 kg of water falls straight down into the box-car. The velocity of the box-car after the water falls into the box-car is

• Option 1)

7.01 m/s.

• Option 2)

6.55 m/s.

• Option 3)

5.02 m/s.

• Option 4)

3.87 m/s.

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As we discussed in

Perfectly Inelastic Collision -

$\fn_jvn v= \frac{m_{1}v_{1}+m_{2}v_{2}}{m_{1}+m_{2}}$

- wherein

Two bodies stick together after the collision ,so there will be a final common velocity (v)

$\fn_jvn m_{1},m_{2}= masses$

$\fn_jvn v_{1}=\: initial \: velocity \: mass\: m_{1}$

$\fn_jvn v_{2}=\: initial \: velocity \: mass\: m_{2}$

$30,000\times 4=31,000v$

$v=\frac{120000}{31000} = 3.87 ms^{-1}$

Option 1)

7.01 m/s.

Incorrect

Option 2)

6.55 m/s.

Incorrect

Option 3)

5.02 m/s.

Incorrect

Option 4)

3.87 m/s.

Correct

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