Final answer:
In physics, to calculate the useful energy transferred by a machine with a 40% efficiency and a 4 kJ energy input, you multiply the total energy input by the efficiency (4000 J × 0.40) to get 1600 J of useful energy.
Step-by-step explanation:
The student's question pertains to the concept of energy efficiency in a mechanical context, which is a topic within the field of physics. To calculate the useful energy that can be transferred by a machine with a given efficiency, we use the formula:
Useful energy output = Total energy input × Efficiency
Given that the machine is 40% efficient and the total energy supplied to the machine is 4 kJ (4000 J), we calculate the useful energy as follows:
Useful energy output = 4000 J × 0.40
Useful energy output = 1600 J
Therefore, the machine can transfer 1600 joules of useful energy.