NCERT Solutions Curiosity Chapter 8 .4 Uniform and Non-uniform Linear Motion — In-text Question
Book page 1178 Updated on2026-09-05
Q1.
Which of the two trains is in uniform linear motion between 10:00 AM and 11:00 AM?
Answer
Train X. Train X covers equal distances in equal intervals of time, so it is in uniform linear motion, while Train Y is in non-uniform linear motion.
Reading the distance column of Table 8.3 for each 10-minute interval:
Interval (10 min each)
Train X — distance (km)
Train Y — distance (km)
10:00 – 10:10
20
20
10:10 – 10:20
20
15
10:20 – 10:30
20
15
10:30 – 10:40
20
25
10:40 – 10:50
20
20
10:50 – 11:00
20
25
Total in 1 h
120 km
120 km
Speed of Train X = 20 km ÷ 10 min = 20 km ÷ (1/6) h = 120 km/h in every interval Train Y: 20 km/10 min = 120 km/h, then 15 km/10 min = 90 km/h, then 25 km/10 min = 150 km/h — the speed keeps changing Average speed of both trains = 120 km ÷ 1 h = 120 km/h
Distance–time graph of Table 8.3. Train X gives a perfectly straight line — uniform motion. Train Y's line bends, because its speed keeps changing.
Why the same average speed does not make them alike: both trains started at 0 km and reached 120 km in one hour, so both have an average speed of 120 km/h. But Train Y reached there by running slow for a while and fast at other times. Average speed tells you about the whole journey; it hides what happened inside it. The graph does not hide it — a straight line means uniform, a bent line means non-uniform.