Exam-style CBSE practice questions on Average Speed & Velocity (Describing Motion). Try each one first, then reveal the correct answer and a step-by-step explanation. Free, from EduLevel — the AI teacher for CBSE.
A cyclist covers a distance of 30 km in 2 hours. What is the speed of the cyclist?
Explanation: Speed = distance ÷ time. Here distance = 30 km and time = 2 hours. So speed = 30 ÷ 2 = 15 km/h.
What is the SI unit of speed?
Explanation: Speed = distance ÷ time. In SI units, distance is measured in metres (m) and time in seconds (s). So the SI unit of speed is m/s. km/h is commonly used in daily life, but it is not the SI unit.
A train moving at a uniform speed covers 120 m in 6 s. What is its speed?
Explanation: Speed = distance ÷ time = 120 ÷ 6 = 20 m/s. Multiplying 120 × 6 = 720 or adding 120 + 6 = 126 are common slips; speed always means distance divided by time.
Which of the following physical quantities has both magnitude and direction?
Explanation: Velocity is speed in a specified direction, so it has both magnitude and direction. Speed, distance and time have only magnitude and no direction. This is why velocity can be zero for a round trip even when speed is not.
A car travels the first 60 km of its journey at 30 km/h and the next 60 km at 60 km/h. What is its average speed for the whole journey?
Explanation: Time for the first part = 60 ÷ 30 = 2 h, and time for the second part = 60 ÷ 60 = 1 h. Total distance = 60 + 60 = 120 km and total time = 2 + 1 = 3 h. Average speed = total distance ÷ total time = 120 ÷ 3 = 40 km/h. Simply averaging 30 and 60 to get 45 km/h is wrong because the car spends different amounts of time at the two speeds.
A bus covers 120 km in the first 3 hours of a journey and then 80 km in the next 1 hour. What is the average speed of the bus for the entire journey?
Explanation: Total distance = 120 + 80 = 200 km. Total time = 3 + 1 = 4 h. Average speed = 200 ÷ 4 = 50 km/h. Averaging the two leg speeds (40 km/h and 80 km/h) to get 60 km/h is incorrect because the bus travels for unequal times at these speeds.
An athlete runs exactly one complete round of a circular track of total length 400 m in 100 s, finishing at the same point where he started. What is the magnitude of his average velocity?
Explanation: Average velocity = displacement ÷ time. Since the athlete returns to his starting point, his displacement is 0 m even though the distance covered is 400 m. So average velocity = 0 ÷ 100 = 0 m/s. His average speed, on the other hand, is 400 ÷ 100 = 4 m/s.
A car is moving at a speed of 72 km/h. What is this speed in m/s?
Explanation: To convert km/h into m/s, multiply by 1000 and divide by 3600, which is the same as multiplying by 5/18. So 72 km/h = 72 × 1000 ÷ 3600 = 20 m/s.
A metro train moves at a uniform speed of 25 m/s. How much distance will it cover in 4 minutes?
Explanation: First convert the time into seconds: 4 minutes = 4 × 60 = 240 s. Distance = speed × time = 25 × 240 = 6000 m = 6 km. Using 4 directly without converting minutes to seconds gives the wrong answer 100 m.
A car covers the first half of the distance between two cities at 40 km/h and the second half at 60 km/h. What is its average speed for the whole journey?
Explanation: Take each half as 120 km. Time for the first half = 120 ÷ 40 = 3 h and time for the second half = 120 ÷ 60 = 2 h. Average speed = total distance ÷ total time = 240 ÷ 5 = 48 km/h. The answer 50 km/h comes from wrongly averaging the two speeds directly, which ignores that the car spends more time at the slower speed.
Starting from his home, a boy runs 3 km due east and then 4 km due north, taking a total time of 1 hour. What is the magnitude of his average velocity?
Explanation: Displacement is the straight-line distance from the starting point to the final point. Since east and north are at right angles, displacement = √(3² + 4²) = √25 = 5 km. Average velocity = displacement ÷ time = 5 ÷ 1 = 5 km/h. His average speed is different: total path ÷ time = 7 ÷ 1 = 7 km/h.
A train has to cover a 60 km journey at an average speed of 40 km/h. It covers the first 30 km at 30 km/h. At what speed must it cover the remaining 30 km?
Explanation: Total time allowed = total distance ÷ average speed = 60 ÷ 40 = 1.5 h. Time already used for the first 30 km = 30 ÷ 30 = 1 h. So the remaining 30 km must be covered in 1.5 − 1 = 0.5 h, which requires a speed of 30 ÷ 0.5 = 60 km/h. Picking 50 km/h so that the two speeds average to 40 is the classic mistake, because average speed is not the mean of the two speeds.
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