Question

Difficulty: MediumScalars and Vectors

Match each physical scenario or vector operation on the left with its corresponding physical property or resultant classification on the right.

  • A particle moving in a circular path at a constant speed of 10 m s110\text{ m s}^{-1}A vector quantity of constant magnitude but continuously changing direction
  • The dot (scalar) product of force and displacement vectorsA scalar quantity representing work done
  • Two forces of equal magnitude PP acting on a point at an angle of 120120^\circ to each otherA single resultant vector of magnitude equal to PP
  • The slope of a displacement-time graphA vector quantity representing velocity

Answer

Particle in uniform circular motion pairs with a vector quantity of constant magnitude but changing direction; Dot product of force and displacement pairs with a scalar quantity representing work done; Two equal forces at 120 degrees pair with a resultant magnitude equal to P; Slope of displacement-time graph pairs with a vector quantity representing velocity.
Each physical scenario correctly corresponds to its fundamental vector/scalar classification or calculated resultant based on vector algebra.

Step-by-Step Solution

1
Analyze circular motion at constant speed
The velocity vector changes direction at every point, giving rise to centripetal acceleration directed toward the center.
Any physical quantity with direction is a vector quantity.
2
Evaluate the product of force and displacement vectors
W=Fd=FdcosθW = \mathbf{F} \cdot \mathbf{d} = F d \cos\theta, producing a scalar quantity (work done).
The dot product of two vectors yields a scalar.
3
Calculate the resultant of two equal vectors PP at 120120^\circ
R=P2+P2+2P2cos120=2P2P2=PR = \sqrt{P^2 + P^2 + 2P^2 \cos 120^\circ} = \sqrt{2P^2 - P^2} = P.
Vector addition follows the law of cosines taking spatial angle into account.
4
Determine the physical quantity represented by the gradient of a displacement-time graph
\text{Slope} = \frac{\Delta s}{\Delta t} = v \text{ (velocity)}.
Displacement per unit time is velocity, a vector quantity.

Key Concept

Scalars, Vectors, and Vector Addition Laws
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