1. In which of the following cases is work done on the object?

A. Lifting an object off the floor.
B. Pushing an object, but it does not move
C. Carrying an object at a constant velocity
D. None of these

2. The energy of a system increases when
A. a force is applied to it
B. it does work on the environment
C. The environment does work on it.
D. None of these

3. The energy of a system decreases when
A. it does work on the environment
B. a force is applied to it
C. the environment doe work on it
D. none of these

and your thinking?

To determine the correct answers, let's understand the concept of work and energy:

1. Work is defined as the transfer of energy that occurs when a force is applied to an object and the object is displaced in the direction of the force. Therefore, work is done only when an object moves. We can use this understanding to evaluate the given options:

A. Lifting an object off the floor - Work is done because an object is being lifted and displaced in the direction of the force applied. So, the answer is A.

B. Pushing an object, but it does not move - In this case, since the object does not move, there is no displacement, and thus no work is done. So, the answer is not B.

C. Carrying an object at a constant velocity - When an object is carried at a constant velocity, there is no change in position, and no displacement occurs over time. Therefore, no work is done. So, the answer is not C.

D. None of these - Since we have determined that work is done in option A, the correct answer is not D.

2. The energy of a system increases when:
A. a force is applied to it - When a force is applied to a system, it can cause a change in its energy. So, the answer is A.

B. it does work on the environment - When a system does work on the environment, it transfers some of its energy to the surroundings. So, the answer is B.

C. The environment does work on it - If the environment does work on the system, then energy is transferred to the system, increasing its energy. So, the answer is C.

D. None of these - Since we have identified that the energy of a system increases in options A, B, and C, the correct answer is not D.

3. The energy of a system decreases when:
A. it does work on the environment - When a system does work on the environment, it transfers some of its energy to the surroundings, leading to a decrease in the system's energy. So, the answer is A.

B. a force is applied to it - When a force is applied to a system, it can cause a change in its energy. However, it might increase or decrease the energy, depending on the circumstances. Therefore, the answer is not B.

C. the environment does work on it - If the environment does work on the system, then energy is transferred to the system, increasing its energy. So, the answer is not C.

D. None of these - Since we have identified that the energy of a system decreases in option A, the correct answer is not D.

In summary, the correct answers are:
1. A. Lifting an object off the floor
2. A. a force is applied to it, B. it does work on the environment, C. The environment does work on it
3. A. it does work on the environment