# NCERT Solutions Class 7 Science Solutions for Exercise in Chapter 13 - Motion and Time

Question 19 Exercise

A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. The total distance covered by the car is:

(i) 100 km (ii) 25 km (iii) 15 km (iv) 10 km

The answer is (ii) 25 km

Calculation:

When the speed of the car is 40 km/h

Time taken = 15 min = 15/60 = 0.25 h

Distance covered d1 = speed x time taken

= 40 x 0.25 = 10 kms

When the speed of the Car is 60 km/ h

Distance covered d2 = speed x time taken

= 60 x 0.25= 15 kms

Total distance covered by the car = d1 + d2

= 10 + 15

= 25 kms

Video transcript
"hello everyone i am sumanjali science tutor from lido learning welcome to the question and answer session in our today's question there is a problem given a car moves with a speed of 40 kilometer per hour for 15 minutes and then with a speed of 60 kilometer per hour for the next 15 minutes the total distance covered by the car is dash we need to find out the distance so before going to the answer let us have an idea about what is a speed so speed is nothing but so speed is nothing but it was the distance covered by distance covered in time we can calculate speed by using formulae speed is equals to distance divided by time and the unit of speed is kilometer per hour or meter per second also we can calculate in meter per second also but in the given question the speed was given in 40 kilometer per hour and 60 kilometer per hour so we are taking speed uh speed units in kilometer per hour in this the distance units are in kilometer and the time units are in hour let us move to the question a car moves with a speed of 40 kilometer per hour so let us consider a car starting point here as a okay so car is moving moving with a speed of 40 kilometer per hour up to point b so here speed is given speed is equals to 40 kilometer per hour for for 15 minutes so time is equals to 15 minutes and this is point b from point b uh car is again started and it reaches to point c and it reaches to point c with a speed of with a speed of 60 kilometer per hour for time is equals to 15 minutes in both the cases we need to calculate a distance so we can take distance 1 as d1 and distance 2 as d2 okay so from the formulae from the formula the distance is in kilometer and the time is in hour so but here the time given uh in 15 minutes so we need to convert this time into our okay so time is equal to 15 minute and we need to if we want to convert this into our so we need to divide it with 60 because 1 hour is equals to because 1 hour is equals to 60 minute so 1 minute is equal to 1 minute is equal to 1 divided by 60 so that 15 minute is equals to 15 divided by 60 so 15 divided by 60 15 ones are 15 fours are 15 so 1 divided by 4 it is equals to 0.2525 hour and in the second case and in the second case time is equals to this is in the first case this is in the second case time is equals to here also it is 15 minutes 15 divided by 60 same 0.25 hour okay now let us calculate distance one okay so distance one distance is equals to distance is equals to speed multiplied by time speed multiplied by time for first case for first case d1 is equals to its speed value 40 multiplied by time value 0.25 so if you multiply this we will be getting we will be getting 10 kilometer and in the second case d2 is equals to 60 multiplied by 0.25 that is 60 multiplied by 1 by 4 1 by 4 so four ones are four fifteen zero four ones are four four fifteen zero sixty so it is fifteen kilometer so now the total distance total distance is equals to ten plus fifteen kilometer is equals to 25 kilometer is the answer so given total distance covered by car is 25 kilometer is answer if you have further queries reach us at the comment section and please subscribe to our channel leader learning question and answer for further queries thank you"
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