Filiberto Amauty: The reason is that this problem involves a rolling object.When you learn about rotation, you will understand that rolling objects involve a "rotational' kinetic energy. Therefore it is much simpler to deal with momentum(mass x velocity).Momentum is conserved regardless of changes in energy.I hope this helps....Show more
Ambrose Mumma: Intially, the cart has mass 250kg. After 2 hours, it has mass 270 kg. Using the conservation of momentum.(250 kg)(3.00 m/s)=(270 kg)(vf)and vf=2.78.Initial KE = ½ * 250 * 3^2 = 1125 JFinal KE = ½ * 270 * 2.78^2 = 1043.334 JDecrease of KE = 81.666 JSome force is causing the kinetic energy of the wagon to decrease.If you drop a marble into a moving wagon, the marble will roll to the back of the wagon. When the marble collides with the back wall of the wagon, the back wall of the wagon will exert a forward force on the marble. During the collision, this force will cause the marble to accelerate in the horizontal direc! tion. According to Newton’s third law, the marble will exert a force of the same magnitude on the back wall of the wagon. During the collision, this force will cause wagon to decelerate. The rain drops are like small marbles. The wagon is moving horizontally and the rain is moving horizontally. As rain drops fall into the wagon, they slide toward the rear of the wagon. . When the rain drops collide with the back wall of the wagon, the back wall of the wagon will exert a forward force on the rain drops. During the collision, this force will cause the rain drops to accelerate in the horizontal direction. According to Newton’s third law, the rain drops will exert a force of the same magnitude on the back wall of the wagon. During the collision, this force will cause wagon to decelerate. During the collision, this force caused velocity of the wagon to decrease from 3.00 m/s to 2.78 m/s.During the collision, this force caused horizontal velocity of the rain drops to increase! from 0 m/s to 2.78 m/s....Show more
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