An open window is shown in top view. It has a locking lever L which holds the window pane at only position R. Which locking lever out of the given options will make it possible to hold the window pane at position P, Q, R and S?
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In mechanical reasoning problems, first address the primary functional requirements (e.g., the number of notches). If multiple options satisfy this, consider the geometry of motion. If the physics seems to contradict the answer, look for other design principles like simplicity, consistency, or ergonomics that might be guiding the question.
Step 1: Rule out A by notch count.
Four positions, P, Q, R and S, need four notches; option A has only three, so it is eliminated first.
Step 2: Compare the remaining options against L's own bend direction.
The original lever L curves, concave toward the hinge, which is what lets it hook over a fixed sill pin and release cleanly as the window swings open and shut.
Step 3: Check B and C against this curve.
Option B is straight, with no concavity at all, so it would not hook over the pin the same way; option C curves the opposite way, convex rather than concave, which also breaks the hooking action.
Step 4: Confirm D.
Option D keeps the same concave curve as L, simply extended with a fourth notch, so it hooks over the pin correctly at all four positions.
\[ \boxed{\text{D}} \]
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Approach Solution -2
A third way to look at this is purely through how the lever has to function mechanically, hooking over one fixed pin while the window itself swings to different angles.
A: With only three notches, this lever cannot even offer a locking position for all four required openings, regardless of its bend.
B: A straight lever has no concave curve to catch and hold the pin securely as the window's angle changes, so it risks slipping off the pin rather than hooking onto it.
C: A lever curving away from the hinge opens its notches outward, in the wrong direction to hook onto a pin that always sits on the same side, so it would not hold the window at all four positions reliably.
D: This lever keeps the same inward, hook-like curve as the original L, so each of its four notches can catch the sill pin the same secure way L's single notch did.
Only D preserves the concave, hook-like curve needed to hold the window pane securely at all four positions.
