Q.The average work done by a human heart while it beats once is 0.5 J. Calculate the power used by heart if it beats 72 times in a minute.

The key idea is that power is the rate of doing work, and the period is the time for one beat.

Step 1 — Find the time for one beat.

If the heart beats 72 times in 60 seconds, the time for one beat (the period $T$) is

Step 2 — Relate work per beat to power.

Power is work done per unit time:

$P = \frac{W}{T}.$ …

Concept First: Frequency and Period

When a process repeats — like a heartbeat — we talk about its frequency (how many times it happens per second) and its period (the time for one cycle). Power, being work per unit time, connects naturally to these ideas.

If you know the work done in one beat and how many beats occur in a given time, you don't need to time a single beat. You just find the total work over a convenient interval and divide by that interval. That's the cleanest route here.

Step-by-step solution

1. Find the total work done in one minute. The heart does 0.5 J of work each time it beats. In one minute, it beats 72 times. Total work = work per beat × number of beats

2. Convert the time interval to seconds. Power is measured in watts (J/s), so time must be in seconds.

3. Apply the definition of power. Power = work done ÷ time taken …

Concept: Power from Repeated Work Events

When work is done repeatedly (once per cycle), total power equals total work over an interval divided by that interval — you don't need the duration of a single cycle if you know how many cycles occur in a known time.

Step 1: Find the total work done in one minute

Each beat does $W_1 = 0.5$ J of work; there are 72 beats in 60 s:

$W_{total} = 0.5 \times 72 = 36\ \text{J}$ …