**Answer: The machine is using an efficiency of 9.9%**

**Explanation:**

**Efficiency = (work output/work input)*100%**

**Work input **= 650Kcal = 650*4184J = **2719600J**

work output = Force * distance

force = mass *acceleration , where mass = 150lb or 68.04kg, a = 10ms⁻²

force = 68.04*10 = 680.4N

distance = velocity * time (in seconds)

velocity = 65 steps/min * (1/60) = 1.083 steps/s

multiply 1.083 steps/s by the height of each step ( in meters) to obtain velocity in units of m/s.

1.083 * 0.2032m = 0.220m/s

**Note: 8.00 inches = 0.2032m**

distance moved = 0.220*1800s = 396m

<em>Note: 30 minutes = 1800s</em>

Therefore, **work output** = 680.4*396 = 269438.4J

Efficiency = (269438.4J/2719600J)*100%

**Efficiency = 9.9%**