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Physics

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Car A of mass 1200kg traveling at 10m/s , collided in too the back of the car B, which is stationary. Following the collision,. The two cars stick together and travel at 6m/s. What is the mass of a car B?

May 20, 2021

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Conservation of momentum is the idea here; momentum, the product of mass and velocity, does not change. Since car B is stationary (velocity=0), the momentum before collision is the mass of car A times its velocity, i.e. (1200 kg)(10 m/s). After the collision the cars are moving together at 6 m/s, so the momentum after collision is (1200 kg +$${m}_{B}$$kg)(6m/s), where $${m}_{B}$$ is the mass of car B. We need to solve the equation

$$(1200+{m}_{B})(6)=(1200)(10).$$

Distributing and isolating $${m}_{B}$$, results in

$$6{m}_{B}=12000-7200=4800, or \ {m}_{B}=\frac{4800}{6}=800 kg.$$

May 20, 2021