Question

Runner A is initially 7.0 mi west of a flagpole and is running with a constant velocity of 5.0 mi/h due east. Runner B is initially 2.0 mi east of the flagpole and is running with a constant velocity of 4.0 mi/h due west. How far are the runners from the flagpole when they meet?

Answer 1

Answer on Question #54677, Physics Mechanics - Kinematics - Dynamics

Runner A is initially 7.0 mi west of a flagpole and is running with a constant velocity of 5.0 mi/h due east. Runner B is initially 2.0 mi east of the flagpole and is running with a constant velocity of 4.0 mi/h due west. How far are the runners from the flagpole when they meet?

Solution

Fig.1

The time from start to meetings (see Fig.1)

$$t = \frac {A B}{V _ {A} + V _ {B}} = \frac {7 m i + 2 m i}{5 m i / h + 4 m i / h} = 1 h$$

where $AB$ is the distance between runners; $V_{A}, V_{B}$ are the speeds of runners.

Distance from the flagpole to the meeting place

$$x = 7 \mathrm{mi} - V _ {A} \cdot t = 7 \mathrm{mi} - 5 \mathrm{mi} / h \cdot 1 h = 2 \mathrm{mi}$$

Answer: $x = 2 \, \text{mi}$

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