Two carts are rolling directly towards each other. They collide and stick togeth

Question

Two carts are rolling directly towards each other. They collide and stick together with no further movement. What can one conclude was true before they collided? a. The cars had equal masse b. The cars had equal speeds. c. The cars had equal kinetic energies. d. The cars had momenta which were equal in magnitude. ~ e. none of the above A 40-kg boy runs and jumps onto a stationary skateboard of mass 3.0 kg. If the boy had a horizontal speed of 5.0 m/s just before he jumps on, what is the speed of the boy and the skateboard immediately after he jumps on? a. 4.6 m/s b. 4.8 m/s c. 5.0 m/s d. 5.4 m/s e. 67 m/s

Explanation / Answer

As there is no further movement in the cars means the final momentum is zero, so initial momentum should also be zero and it is possible only when the two carts are initially having equal and opposite momenta. Means option (d) is correct

Initial momentum of boy + skateboard

= final momentum of boy + skateboard

40 × 5 + 0 = (40 + 3)v = 43v

Hence speed of skateboard with boy = 200/43 = 4.6 m/s

Means option a is correct

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