An object moves in a straight line with uniform motion and covers 180 km in 6 hours. What is its speed? Choose from 900 m/s, 30 km/h, 900 km/h, 30 m/s.

Step-by-step solution

1. 1

   Identify the motion type. "Uniform motion" means the speed never changes, so the single formula $v=\dfrac{s}{t}$ applies to the whole trip — no averaging over segments is needed.

2. 2

   Match the units before dividing. The distance is already in kilometres and the time in hours, so the quotient will come out directly in $\text{km/h}$ with no conversion inside the division.

3. 3

   Divide distance by time. $v=\frac{s}{t}=\frac{180\text{ km}}{6\text{ h}}=30\text{ km/h}$

4. 4

   Convert to SI to test the distractors. $30\text{ km/h}=\dfrac{30\times 1000}{3600}\text{ m/s}\approx 8.33\text{ m/s}$. So option D ($30\text{ m/s}$) is the same number attached to the wrong unit, and option C ($900$ km/h) is $30$ times too large, and option A ($900$ m/s) carries that same wrong number with the wrong unit as well — $108$ times the correct $8.33$ m/s.

5. 5

   State the answer. Only option B survives: the speed is $30\text{ km/h}$.