Paper 2 · November 2019 · Physics
Fig. 5.1 shows one stroke in the operation of a four stroke engine. Which stroke is shown, and what shows it?
AThe exhaust stroke, because the exhaust valve is open while the piston moves up.
BThe power stroke, because both valves are closed and the piston is being driven down.
CThe induction stroke, because the inlet valve is open while the piston moves down.
DThe compression stroke, because both valves are closed while the piston moves up.
Explanation
The stroke is read from two things: whether the valves are open or closed, and which way the piston is travelling. With both valves shut and the piston moving down, the burning mixture is expanding and pushing the piston, which is the power stroke.
Derived from ZIMSEC Combined Science 4003/2, November 2019, Q5(a)