Page 23 - Physics Coursebook 2015 (A level)

Chapter 1: Kinematics – describing motion
QUESTIONS
16 A swimmer can swim at 2.0 m s−1 in still water. She aims to swim directly across a river which
is flowing at 0.80 m s−1. Calculate her resultant velocity. (You must give both the magnitude and the direction.)
17 A stone is thrown from a cliff and strikes the surface of the sea with a vertical velocity of
18 m s−1 and a horizontal velocity v. The resultant of these two velocities is 25 m s−1.
a Draw a vector diagram showing the two velocities and the resultant.
b Use your diagram to find the value of v.
c Use your diagram to find the angle between the stone and the vertical as it strikes the water.
Summary
■■ Displacement is the distance travelled in a particular direction.
■■ Velocity is defined by the word equation velocity = change in displacement
time taken
The gradient of a displacement–time graph is equal to velocity:
velocity = Δs Δt
■■ Distance and speed are scalar quantities. A scalar quantity has only magnitude.
■■ Displacement and velocity are vector quantities.
A vector quantity has both magnitude and direction.
■■ Vector quantities may be combined by vector addition to find their resultant.
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