First slide

Collisions

Question

A mass of 20 kg moving with a speed of 10m/s collides with another stationary mass of 5 kg. As a result of the collision, the two masses stick together. The kinetic energy of the composite mass will be

Moderate

A

600 Joule
B

800 Joule
C

1000 Joule
D

1200 Joule

Solution

$m_{1} v_{1} + m_{2} v_{2} = (m_{1} + m_{2}) v_{sys.}$
$20 \times 10 + 5 \times 0 = (20 + 5) v_{sys.} \Rightarrow v_{sys.} = 8 m / s$
K.E. of composite mass $= \frac{1}{2} (20 + 5) \times {(8)}^{2} = 800 J$

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