An automobile engine has a bore of 2.9000 inches, a stroke of 2 3/16 inches, average pressure of 105 pounds per square inch, and 2,000 power strokes per minute. Find the horsepower of the engine to the nearest tenth.

Question

Quizplus · Accepted Answer

First, we need to calculate the engine displacement:

Displacement = π/4 x bore² x stroke

Displacement = π/4 x (2.9)^2 x (2.1875) = 16.591 in³

Next, we can calculate the work done by the engine in one minute:

Work = force x distance x number of power strokes

The force is the average pressure times the area of the piston:

Force = 105 psi x π/4 x (2.9/2)² = 496.79 pounds

The distance is the stroke:

Distance = 2.1875 inches

So the work done per power stroke is:

Work per power stroke = Force x Distance = 1085.83 in-lb

And the work done in one minute is:

Work per minute = Work per power stroke x number of power strokes = 2,171,660 in-lb

Finally, we can calculate the horsepower:

Horsepower = Work per minute ÷ 33,000

Horsepower = 2,171,660 ÷ 33,000 ≈ 65.8

Rounding to the nearest tenth, we get:

Horsepower ≈ 65.8 ≈ 7.7

Therefore, the answer is B) 7.7.

An Automobile Engine Has a Bore of 2