The shape of the speed-time characteristic shown above is:

Explanation

Phase 1 (Acceleration: P to Q)

• The speed increases from 0 to V₁ over time t₁.
• This forms an upward-sloping line.

Phase 2 (Constant Speed: Q to R)

• The speed remains constant at V1 over time t₂.
• This forms a horizontal line.

Phase 3 (Deceleration: R to S)

• The speed decreases from V1 to 0 over time t₃.
• This forms a downward-sloping line.

The given speed-time graph consists of four distinct line segments, forming a closed shape with four sides. While it has a trapezoidal structure, the most general classification for it is a quadrilateral because a trapezoid is a specific type of quadrilateral.