This is true that the system is an open system because the total mechanical energy of the system is not constant, which means that an external force removed 140 j of mechanical energy. this can also be a closed system if there is only exchange of energy.
An open system can exchange energy and matter both with its surrounding. One example is the stovetop which releases heat water vapor to the surrounding.
A closed system can exchange only energy with surroundings, not matter. A tightly-fit container is an example of a closed system.
An isolated system can't exchange energy or matter with its surroundings. An insulated drink cooler can be thought of as an isolated system. A truly isolated system can't be obtained.
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