91影视

When an object A moves with velocity${\stackrel{鈫�}{v}}_{\mathrm{AB}}$with respect to another object B and object B moves with velocity${\stackrel{鈫�}{v}}_{\mathrm{BC}}$with respect to another object C along the same line, the relative velocity of A with respect to C is given as:

${\stackrel{鈫�}{v}}_{\mathrm{AC}}={\stackrel{鈫�}{v}}_{\mathrm{AB}}+{\stackrel{鈫�}{v}}_{\mathrm{BC}}$

If the forward direction, i.e., the direction of motion of the ship, is taken as the positive direction, then:

The velocity of the person jogging toward the bow of the ship with respect to the ship is ${\stackrel{鈫�}{v}}_{\mathrm{ps}}=2.0{\mathrm{ms}}^{-1}$.

The velocity of the person jogging toward the stern of the ship with respect to the ship is ${\stackrel{鈫�}{v}}_{\mathrm{ps}}=-2.0{\mathrm{ms}}^{-1}$.

The velocity of the ship with respect to the water is ${\stackrel{鈫�}{v}}_{\mathrm{sw}}=8.5{\mathrm{ms}}^{-1}$.

Let the velocity of the person relative to the water be ${\stackrel{鈫�}{v}}_{\mathrm{pw}}$.

Since both the person and the ship are moving along the same line, their velocities will add up. Thus, thevelocity of the person relative to the water will become:

$\begin{array}{c}{\stackrel{鈫�}{v}}_{\mathrm{pw}}={\stackrel{鈫�}{v}}_{\mathrm{ps}}+{\stackrel{鈫�}{v}}_{\mathrm{sw}}\\ =\left(2.0+8.5\right){\mathrm{ms}}^{-1}\\ =10.5{\mathrm{ms}}^{-1}\end{array}$

Thus, the velocity of the jogger relative to the water is $10.5{\mathrm{ms}}^{-1}$in the forward direction.

Now, the jogger is moving toward the stern of the ship. Therefore thevelocity of the person relative to the water will now become:

$\begin{array}{c}{\stackrel{鈫�}{v}}_{\mathrm{pw}}={\stackrel{鈫�}{v}}_{\mathrm{ps}}+{\stackrel{鈫�}{v}}_{\mathrm{sw}}\\ =\left(-2.0+8.5\right){\mathrm{ms}}^{-1}\\ =6.5{\mathrm{ms}}^{-1}\end{array}$

Thus, the velocity of the jogger relative to the water is $6.5{\mathrm{ms}}^{-1}$in the forward direction.