SRI BASARA LEADS SCHOOL basic IIT PHYSICS Class day13

Added: 2026-05-15

[00:00:13]I got that was first of a distance.

[00:00:22]First of a distance.

[00:00:27]The speed the speed 10 kilome per hour.

[00:00:40]Okay.

[00:00:43]Second third.

[00:00:50]second/ third of a distance.

[00:00:59]The speed the speed 20 kilome per hour.

[00:01:11]And last third.

[00:01:18]Last third the speed of a speed of 60 kilome per hour.

[00:01:33]60 kilome per hour. Then find the average speed.

[00:01:40]Find the average speed of the car.

[00:01:45]Find the average speed of the car.

[00:01:55]Find the average speed of the car over the entire distance.

[00:01:59]Note of the problem.

[00:02:02]The second third how much it is? 20 km/h. And last third with a speed of 60 kilome. Find the speed of the car over the entire distance. So this is the problem.

[00:02:16]What is the formulas of this problem?

[00:02:17]What is the problem for you? We have to use V3 V1 V2 V3.

[00:02:28]>> Yes. Okay. The formula is why we have to use this formula.

[00:02:37]has three distances.

[00:02:38]>> Yes, three equal distances. Three equal distances in the first third 10, second third 20, last third 60. Let us consider this is the total distance. We don't know the total distance but this distance is divided into three.

[00:02:57]For first it is traveling with the speed of 10 km per hour.

[00:03:05]Second third it is traveling with a speed of 20 kilome per hour and last third it is traveling with a speed of 60 kilome per hour. So we have to find the average speed and we know the formula.

[00:03:25]Yes, we know the formula of average speed.

[00:03:29]It is total and we know the what is total distance here 2 3 3 V1 V2 V3 51 V2 >> V1 V2 plus V2 V3 plus V3 V. So this is the formula and we know the How to der this formula we write yesterday? Okay. So what is average?

[00:04:03]So also we try to write this v. We can write v. Okay. So v average is equals to what is v_sub1 here?

[00:04:15]>> What is v_sub_1?

[00:04:16]>> V1.

[00:04:18]>> What is v_sub1?

[00:04:18]>> 10.

[00:04:19]>> What is v_sub1?

[00:04:20]>> 10.

[00:04:21]>> 10.

[00:04:23]What is v_sub_2?

[00:04:25]>> What is v_sub3?

[00:04:28]>> 5 10 into >> + 10 into 20 >> plus 20 into 60 >> plus 60 into 10 or 10 into 60. A = B= A to B is equals to B into B then 67. So 0 0 0 >> 3 zeros 1 2 3 zeros 36 >> 6 2's are 12 1's are >> 12 3's are >> 36 it is 36 that is 36 0 0 36,000 >> 36,000 >> 2 1 Z200 that is 200 >> plus 0 0 6 2's are 12 that is 1200 again 0 0 6 1 6 600 So 1200 + 200 1400 40 + 6 15,000 so 36,000 by 2,000 and you know 0 0 0 that means 80ome per So this is the average speed and this is the one method. What is another method to do this problem?

[00:06:00]>> Yes.

[00:06:02]>> You can use average speed. You know the formula n= >> n by average speed= 1 v1 v2.

[00:06:18]Okay. Here n is equals to how much?

[00:06:21]Three >> because 3= N is = 3 N = So the average speed is 3 average speed is equals to 1 by V1. What is V1? 10 1 by V2 that is 1 by V3 that is 60. What is the LCM of 10 20 60? 60 is the 10 6 23 are 60. So 60 is the LCM.

[00:06:48]Okay. 10 6 are 23 are 61.

[00:06:55]Okay. Uh 10 by 60. 10 by 60.

[00:07:01]10 by 60. So 1 by 6.

[00:07:06]So we'll get 3 by average speed is equals to 1 by 6. Cross multiplication average speed into 1.

[00:07:16]Average speed average speed 1 is equals to 6 into 3 that is 18.

[00:07:25]>> So the average speed is equals to 18 kilome per hour.

[00:07:36]If anybody asks 18 km is equals to how many m/s.

[00:07:43]So that note >> 18 kilome per hour is = into then 180 m per hour is equals to 18 into 5 by 18.

[00:08:04]What is it?

[00:08:06]become five%.

[00:08:09]That means 18 kilome per hour is equals to 5 m.

[00:08:19]And we have another method also only this problem.

[00:08:24]Okay. Okay. Right.

[00:08:33]As you know the uh total distance I'm considering the total distance S.

[00:08:39]Let us say from initial point to find point A to B.

[00:08:44]Okay. Now the total distance is nothing but S. I'm considering the total distance as S.

[00:08:51]So it can be splitted and divided into three equal parts. So that this distance becomes S by 3. Right.

[00:08:59]This is also s also s.

[00:09:03]What is the total distance? S 3 + s by 3 + s by 3 that becomes 3 s by 3 that is equal to s. So total distance is this.

[00:09:14]So it can be divided into three equal position equal parts. S3 s3 s. So first part travels with a speed of 10 kilome per hour.

[00:09:29]Second part.

[00:09:31]Second part.

[00:09:36]Second part. V2 is equals to it is 20 kilome per hour. And third part V3 is equals to 60 kilome per hour.

[00:09:52]Okay. What is the average speed?

[00:10:00]What is average speed?

[00:10:04]Overage speed is equals total distance total distance by Total.

[00:10:19]Total distance by total length.

[00:10:27]Total distance total. Okay. How much total distance it is?

[00:10:33]This is the total distance right. So average speed that is V average is equals to what is the total distance? S by time. What is the total time?

[00:10:44]Since speeds are different in three different parts speeds are different as we know that speed is different speed is different time will be different. So that three equal sorry three different time that is t1 plus t2 plus t3 for the first part the time taken by the body to complete this is t1. For the second part the time taken by the time taken by the car to complete the second part is t2.

[00:11:11]The time taken by the car to complete the third part is T3. So three different times. Why? Because three different times because three different speeds.

[00:11:19]Car moving with three different speeds.

[00:11:21]Speeds are different. As we know the times will be different. Okay. So t1 t we have to find the time separately. As we know that times uh we know that time is equals to what?

[00:11:35]What is the formula for time?

[00:11:38]>> That is distance by speed. Time is nothing but distance by >> for the first time.

[00:11:47]First part what is the time for the first part? What is the time?

[00:11:55]What is the time for the first part?

[00:12:05]For the first part. So t1 is equals distance basically. What is the distance?

[00:12:10]>> S by 3 by V1. Okay. After the we substitute. Okay.

[00:12:20]>> So, T1 is equals to S by 3 V1.

[00:12:26]TS2 is equals S by 3 by V2.

[00:12:32]That is T2 is equals to S by 3.

[00:12:37]Similarly, Similarly, t3 is equals to how much?

[00:12:47]>> Sx3 by SX3 by >> W.

[00:12:54]So that P3 is equals to S by 3 V3 S by >> 3 V3.

[00:13:05]Okay. So this is equation one equation two.

[00:13:12]This is equation three.

[00:13:16]Now substitute substitute equations >> 2 3 and four >> in one.

[00:13:33]What we get? P average is equals to S by T1. What is T1?

[00:13:42]S by 3 V1. What is T2? S by >> 3 V1. What is T3? S by >> 3 V s.

[00:13:55]>> Yes.

[00:13:57]S is common. S3 taken as common.

[00:14:10]So the V R is equals to S by S by 3 is taken as common V1 V2 S3.

[00:14:31]Yes sir.

[00:14:32]>> 1x 3.

[00:14:33]>> So 1 by 1 >> 1x 3 into 1 by 10 >> + 1 by 1 + 1 by 60.

[00:14:46]Okay. What is the LCM?

[00:14:51]>> 60 is the LCM again. 10 60 >> 23 are 1 again. 1 by 1 by 3 >> 10 by 60 0 cancel.

[00:15:07]>> So 0 0 cancel. So this is 1 by 1 by 18.

[00:15:13]So reciprocal >> 18 kilome per hour. So that is the average speed.

[00:15:25]So any method you can choose any method you get the same answering kome.

[00:15:33]Okay.