Study the scenario.
Two trains are moving along a train track at 45 mph towards each other. The first train has twice the mass of the second train. The trains spot each other, and apply the brakes at the same time. Both come to a stop, and disaster is narrowly averted.
Which of the following choices correctly describes the work done in the situation?
No work was done on the trains because an external force was applied to the trains in order to change their velocity. Only the velocity changed, no change in displacement occurred.
No work was done on either train because the force applied to each train was not in the same direction as their motion.
Work was done on the two trains because the trains gained kinetic energy as they slowed down. The first train had the most work done on it.
Negative work was done on both of the trains because a force was applied over a distance in order to change their velocity, and the forces were applied in a direction opposite to their motion.
is it the third one?
is it the last one?
Yes, the third option correctly describes the work done in this situation.
To find the answer, we first need to understand the concept of work. Work is defined as the force applied on an object multiplied by the displacement of the object in the direction of the force. It is a measure of the energy transferred to or from an object.
In this scenario, both trains are moving towards each other, so their direction of motion is opposite. When the brakes are applied, a force is exerted on each train to slow them down.
However, it's important to note that work is only done when there is a displacement in the direction of the force. In this case, the trains come to a stop, so their displacement is zero. Therefore, no work is done on either train in terms of their displacement.
But, work is done to change their kinetic energy. As the trains slow down, their kinetic energy decreases. According to the work-energy principle, the work done on an object is equal to the change in its kinetic energy. So, in this scenario, work is done on the trains because their kinetic energy is reduced as they slow down.
Additionally, the first train, which has twice the mass of the second train, will experience more work done on it. This is because the work done is directly proportional to the mass of the object.
Hence, the correct answer is: "Work was done on the two trains because the trains gained kinetic energy as they slowed down. The first train had the most work done on it."