Dheema ya Tez: Chaal

Class 7 Science · Chapter 8: Samay aur Gati ka Maapan · NCERT Curiosity section 8.2–8.3

Seekho

100 m daud mein Ishaan, Kabir aur Neel saath shuru karte. Kuch second baad Kabir aage. Usi samay mein usne zyaada doori tay ki, to wo tez. Par 100 m aur 400 m daud ko kaise milaayein? Ikaai samay mein tay doori nikaalte: chaal.

Chaal = kul doori ÷ kul samay. SI ikaai metre prati second (m/s); sadak par kilometre prati ghanta (km/h). Zoya 15 min mein 3.6 km cycle se school jaati: 3600 m ÷ 900 s = 4 m/s. Kyunki 1 km/h = 1000 m ÷ 3600 s, km/h ko 5/18 se guna karke m/s, aur m/s ko 18/5 se guna karke km/h.

speed = distance ÷ time

Ulat-pulat karke baaki nikaalo: doori = chaal × samay aur samay = doori ÷ chaal. 50 km/h ki bus 2 h mein 100 km; 90 km/h ki train ko 360 km ke liye 4 h. Gaadi ka speedometer km/h mein chaal aur odometer tay doori dikhaata.

distance = speed × time; time = distance ÷ speed

Yaad rakho

• Chaal = doori ÷ samay; ikaai m/s ya km/h (km/h se m/s ke liye × 5/18).
• Doori = chaal × samay; samay = doori ÷ chaal.

Quick check

Car 3 h mein 180 km chalti. Chaal?

1. 60 km/h
2. 540 km/h
3. 183 km/h
4. 6 km/h

Socho

Ghoda 18 m/s se daudta aur train 72 km/h se. Kaun tez?

Practice

Teen levels (easy, medium, hard) ke naye sawaalon se practice karo, kuch hands-on, hints aur hal ke saath. Topic poora karne ke liye pichhle 5 mein se 4 sahi karo.