Question

A person reaches a point directly opposite on the other bank of a flowing river, while swimming at a speed of 5m/s at an angle of 120 degree with the slow. The speed of the flow must be
1. 2.5m/s
2. 3m/s
3. 4m/s
4. 1.5m/s

Answer 1

Answer on Question 48603, Physics, Mechanics | Kinematics | Dynamics

Question:

A person reaches a point directly opposite on the other bank of a flowing river, while swimming at a speed of $5\mathrm{m / s}$ at an angle of 120 degree with the slow. The speed of the flow must be:

1. $2.5\mathrm{m / s}$

2. $3\mathrm{m / s}$

3. $4\mathrm{m / s}$

4. $1.5\mathrm{m / s}$

Solution:

Let's direct x-axis along the river's flow :

$$\left| v _ {x r i v e r} \right| = \left| v _ {x s w i m m e r} \right|,$$ $$\left| v _ {x r i v e r} \right| = \left| v _ {s w i m m e r} \cdot \cos 1 2 0 ^ {0} \right| = \left| 5 \frac {m}{s} \cdot (- 0. 5) \right| = 2. 5 \frac {m}{s}.$$

Answer:

1) The speed of the flow must be $2.5 \frac{m}{s}$ .

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