Class 7 Science Chapter 8 NCERT Solutions Hinglish mein: Measurement of Time and Motion

Curiosity (Reprint 2026-27) ke Chapter 8, Measurement of Time and Motion, ke har sawaal ka jawab: text ke beech ke sawaal aur activities, “Let Us Enhance Our Learning” ke saare 11 sawaal poori working ke saath, aur exploratory projects. Page numbers book ke hisaab se hain (pages 105–120). Activities mein sample readings hain; tumhari thodi alag ho sakti hain. Short notes: Chapter 8 ke notes.

Clock se pehle time naapna (pages 105–107)

Jab clock aur ghadiyan nahi thi tab time kaise naapa jaata tha? Log prakriti ki dohraane waali ghatnaon, jaise sooryoday aur suryast, Chaand ki kalaayein aur mausam, se din aur calendar banaate the. Chhote time ke liye sundial (chalti parchhaai), water clock (bartan se baahar ya andar behta paani), hourglass (ret) aur candle clock (nishaan waali mombatti) istemaal hote the.

Activity 8.1: Tumhara water clock taiyaar hai. Ise kaise istemaal karoge? Neeche waale hisse ka paani waapas upar waale hisse mein daalo. Jaise-jaise wo tapakta hai, neeche waale hisse mein star dekho: har baar wo tumhare kisi nishaan tak pahunche, to ek minute aur beet gaya.

Simple pendulum (pages 109–110)

Kya pendulum Class 6 ke dhaage pe latke rubber jaisa hai? Haan. Dono ek mean position ke aas-paas aage-peeche jhoolte hain, jo oscillatory motion hai, aur dono ek tay samay ke baad apna raasta dohraate hain.

Activity 8.2: Kya tumhara pendulum jhool raha hai? Kya iska time period har baar lagbhag ek jaisa hai? Haan. 100 cm ke pendulum ki sample readings:

Trial	10 oscillations ka time → time period
1	20.1 s → 2.01 s
2	19.9 s → 1.99 s
3	20.0 s → 2.00 s

Time period har baar lagbhag ek jaisa hai, isliye tay lambai ka pendulum har oscillation mein utna hi time leta hai.

Scientist ki tarah socho: agar tum Galileo hote to kya jaanchte? Poochhne laayak sawaal: kya saare pendulums ka time period ek jaisa hai? Kya time period lambai, bob ke mass, ya bob ko kitna kheencha gaya, is pe depend karta hai? Ek baar mein ek cheez badlo. Wahi bob aur alag lambai se time period badalta hai: lamba pendulum dheere jhoolta hai (sample: 25 cm ke liye lagbhag 1.0 s, 50 cm ke liye 1.4 s, 100 cm ke liye 2.0 s). Wahi lambai aur alag mass ke bob se time period nahi badalta. Isliye time period lambai pe depend karta hai, bob ke mass pe nahi.

Time ki units (pages 111–112)

Activity 8.3: Deewaar ke clock se sabse chhota kitna time naap sakte ho? Ek second, yaani seconds ki suyi ka ek nishaan se agle tak jaane ka time.

Ek hi doori ki race mein time batata hai kaun tez hai. Alag-alag doori ki race mein kaise batayein? Speed ki tulna karo, yaani har runner dwara ek unit time mein tay ki gayi doori (kul doori ÷ kul time). Jiski speed zyaada, wo tez.

Speed (pages 113–116)

Activity 8.4: Apne station aur agle station ke beech trains ki speed nikaalo. Timetable se do stations ke beech ki doori lo, chalne se pahunchne tak ka time nikaalo, aur bhaag do. Sample (tareeka dikhaane ke liye banaaye gaye numbers):

Train	Doori, time aur speed
Passenger	30 min (0.5 h) mein 24 km: 24 ÷ 0.5 = 48 km/h
Express	1 h mein 60 km: 60 km/h
Superfast	1 h 30 min (1.5 h) mein 105 km: 105 ÷ 1.5 = 70 km/h

Sabse tez train kaunsi hai? Jo ek unit time mein sabse zyaada doori tay kare, yaani jiski speed sabse zyaada ho: yahan superfast train.

Marathon mein kuch runners ek jaisi speed se chal rahe the aur kuch tez ya dheere ho rahe the. Unki gati mein kya fark tha? Seedhi sadak pe ek jaisi speed rakhne waale runners uniform linear motion mein the, barabar samay mein barabar doori tay karte hue. Tez ya dheere hone waale runners non-uniform linear motion mein the.

Uniform aur non-uniform motion (page 117)

Table 8.3 mein kaunsi train uniform linear motion mein hai? Train X har 10 minute mein 20 km chalti hai, barabar antar mein barabar doori, isliye wo uniform linear motion mein hai. Train Y 20, 15, 15, 25, 20 aur 25 km chalti hai, isliye wo non-uniform linear motion mein hai.

Let Us Enhance Our Learning (pages 118–119)

1. 10 second mein 150 metre chalne waali car ki speed nikaalo. Jawab km/h mein do. Speed = 150 m ÷ 10 s = 15 m/s. km/h mein: 15 m/s = 15 × (1/1000 km) ÷ (1/3600 h) = 15 × 3600 ÷ 1000 = 54 km/h.

2. Ek runner 400 metre 50 second mein poore karta hai. Doosra wahi doori 45 second mein. Kiski speed zyaada hai aur kitni? Pehla runner: 400 m ÷ 50 s = 8 m/s. Doosra runner: 400 m ÷ 45 s = 8.89 m/s (lagbhag). Doosra runner tez hai, 8.89 − 8 = 0.89 m/s se (theek 8/9 m/s).

3. Ek train 25 m/s se 360 km chalti hai. Kitna time lagta hai? 360 km = 360,000 m. Time = doori ÷ speed = 360,000 m ÷ 25 m/s = 14,400 s = 14,400 ÷ 3600 h = 4 h.

4. Ek train 3 h mein 180 km chalti hai. (i) km/h mein speed, (ii) m/s mein, (iii) usi speed pe 4 h mein doori nikaalo. (i) Speed = 180 km ÷ 3 h = 60 km/h. (ii) 60 km/h = 60 × 1000 m ÷ 3600 s = 16.67 m/s (lagbhag). (iii) Doori = 60 km/h × 4 h = 240 km.

5. Daudta ghoda lagbhag 18 m/s tak pahunch sakta hai. 72 km/h ki train se iski tulna kaisi hai? 72 km/h = 72 × 1000 m ÷ 3600 s = 20 m/s. Train (20 m/s) ghode (18 m/s) se 2 m/s tez hai. km/h mein ghode ki speed 18 × 3.6 = 64.8 km/h hai, jo train se 7.2 km/h kam hai.

6. Bina traffic waale seedhe highway pe car aur shahar ke traffic mein car ke udaharan se uniform aur non-uniform motion ka fark batao. Seedhe, khaali highway pe car ek jaisi speed, jaise 80 km/h, rakh sakti hai aur barabar samay mein barabar doori tay karti hai: ye uniform linear motion ke kareeb hai. Shahar ke traffic mein car baar-baar tez hoti, dheemi hoti aur signals aur crossings pe rukti hai, barabar samay mein alag-alag doori tay karti hai: ye non-uniform motion hai.

7. Agar cheez uniform motion mein hai, to table ki khaali jagah bharo. Ye pehle 10 s mein 8 m chalti hai, isliye speed 8 m ÷ 10 s = 0.8 m/s hai, aur ye har 10 s mein 8 m chalti hai.

Time (s)	Doori (m)
0	0
10	8
20	16
30	24
40	32
50	40
60	48
70	56

8. Ek car pehle ghante mein 60 km, doosre mein 70 km aur teesre mein 50 km chalti hai. Kya gati uniform hai? Average speed nikaalo. Gati uniform nahi hai, kyunki car ek-ek ghante ke barabar antar mein alag-alag doori chalti hai. Average speed = kul doori ÷ kul time = (60 + 70 + 50) km ÷ 3 h = 180 km ÷ 3 h = 60 km/h.

9. Rozaana zindagi mein kaunsi gati zyaada aam hai: uniform ya non-uniform? Teen udaharan do. Non-uniform motion kahin zyaada aam hai. Udaharan: school bus jo chalti hai, tez hoti hai, mod pe dheemi hoti hai aur bus stop pe rukti hai; school paidal jaana, crossings pe dheere aur der hone pe tez; cycle jo dhalaan pe tez aur chadhaai pe dheemi chalti hai. Zameen pe ludhakti aur dheemi hoti gend, aur chalti-rukti lift, aur udaharan hain.

10. Cheez ki speed uniform hai ya non-uniform? Average speed nikaalo. Har 10 s mein cheez 6, 4, 6, 5, 8, 6, 7, 3, 10 aur 5 m chalti hai: barabar antar mein alag-alag doori, isliye speed non-uniform hai. Average speed = 60 m ÷ 100 s = 0.6 m/s.

11. Ek gaadi seedhi line pe 2 km chalti hai. Pehle 500 m 10 m/s se aur agle 500 m 5 m/s se. Baaki doori kis speed se chale ki yaatra 200 s mein poori ho? Average speed kya hai? Pehle 500 m ka time = 500 m ÷ 10 m/s = 50 s. Agle 500 m ka time = 500 m ÷ 5 m/s = 100 s. Laga time = 150 s, isliye baaki 2000 − 1000 = 1000 m ke liye 200 − 150 = 50 s bache. Zaroori speed = 1000 m ÷ 50 s = 20 m/s. Poori yaatra ki average speed = 2000 m ÷ 200 s = 10 m/s.

Exploratory Projects (pages 119–120)

1. Aisa tairne waale katore ka water clock banao jo lagbhag 24 minute mein doobe. Ek chhota, halka dhaatu ya plastic ka katora lo, uske tale ke beech mein chhota ched karo, use paani ki baalti mein tairaao, aur doobne ka time naapo. Agar jaldi doobe to bada katora lo ya chhote ched ke saath dobara shuru karo; agar der se doobe to ched thoda bada karo. Har katore aur ched ke size ka note rakho jab tak koi katora lagbhag 24 minute, yaani ek ghatika, mein na doobe.

2. Nabz ki dar naapo aur nabz se time naapo. Kalaai ke andar do ungliyon se nabz dhoondho aur 1 minute tak dhadkanein gino (ya 15 s tak gin kar 4 se guna karo). Har dost ki nabz aaram mein aur jagah pe daudne ke baad likho. Kahaani ka vichaar: church mein Galileo ki tarah, ek ladki ghadi band hone pe apni nabz se jhoolta lamp, tapakta nal ya ek gaana time karti hai.

3. Activity 8.2 mein time period ki readings thodi alag kyun aati hain, aur ise kaise kam karein? Kaaran: ghadi shuru ya band karne mein thodi der, oscillations galat ginna, chhodte waqt bob ko dhakelna, bahut chauda ya ek tal mein na hone waala jhoola, hawa, ya support ka mazboot na hona. Kam karne ke liye: 20 ya zyaada oscillations ka time naapo, bob ko har baar utne hi chhote angle se dheere chhodo, mazboot support lo, bob ke ek hi point se guzarte waqt ghadi shuru aur band karo, har trial mein ek hi vyakti time naape, aur kai readings ka average lo.

4. Playground ke jhoolon ka time period naapo. Jhoole pe halka ya bhaari bachcha baithe, uska time period lagbhag ek jaisa rehta hai, par lambi zanjeeron waale jhoole ka time period lamba hota hai. Isliye haan, jhoola ek pendulum hai: seat aur bachcha bob ki tarah aur zanjeerein dhaage ki tarah kaam karti hain.

5. 100 m, 200 m aur 400 m race ke Olympic winners ki speed ki tulna karo. (Extra: Paris 2024 Olympics ke official winning times.)

Event, Paris 2024	Winning time → speed
Purush 100 m	9.79 s → 100 ÷ 9.79 = 10.21 m/s (lagbhag 36.8 km/h)
Purush 200 m	19.46 s → 10.28 m/s (lagbhag 37.0 km/h)
Purush 400 m	43.40 s → 9.22 m/s (lagbhag 33.2 km/h)
Mahila 100 m	10.72 s → 9.33 m/s (lagbhag 33.6 km/h)
Mahila 200 m	21.83 s → 9.16 m/s (lagbhag 33.0 km/h)
Mahila 400 m	48.17 s → 8.30 m/s (lagbhag 29.9 km/h)

Tokyo 2020 mein purushon ki 100 m 9.80 s (10.20 m/s), purushon ki 200 m 19.62 s (10.19 m/s) aur mahilaon ki 100 m 10.61 s (9.43 m/s) mein jeeti gayi. Dono Games mein 400 m teeno mein sabse dheemi race hai, kyunki koi bhi itni der tak poori taakat se sprint nahi kar sakta. Paris mein purushon ki 200 m ke winner ki average speed 100 m ke winner se bhi zyaada thi, kyunki dheemi shuruaat lambi race ka chhota hissa hoti hai; auraton mein 100 m sabse tez thi.