Power is the rate of energy transfer

Steps:

• Define power as the rate at which work is done or energy is transferred.
• Recall that work or energy has the unit joule (J).
• Note that time has the unit second (s).
• Combine to get power unit as energy per time, or J/s.

Why B is correct:

• Power is defined as P = W/t, where W is work in joules and t is time in seconds, yielding J/s (watt).

Why the others are wrong:

• A: Js represents energy or action, not rate.
• C: Ns represents momentum (force × time).
• D: N/s represents force per time, like thrust rate, not energy rate.

Final answer: B