NCERT Solutions for Class 7 Science Chapter 13

Important NCERT Questions

7th Chapter 13 Motion and Time

NCERT Books for Session 2022-2023

CBSE Board and State Board

Questions No: 5

# The odometer of a car reads 57321.0 km when the clock shows the time 08:30 AM. What is the distance moved by the car, if at 08:50 AM, the odometer reading has changed to 57336.0 km? Calculate the speed of the car in km/min during this time. Express the speed in km/h also.

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Distance covered by car = 57336.0 km – 57321.0 km = 15.0 km

Time taken between 08:30 AM to 08:50 AM = 20 minutes = 20/60 hour = 1/3 hour

So, speed in km/min

Speed= 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑐𝑜𝑣𝑒𝑟𝑒𝑑 / 𝑇𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛 =15 km / 20km = 0.75 𝑘𝑚 / 𝑚𝑖𝑛

Speed= 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑐𝑜𝑣𝑒𝑟𝑒𝑑 / 𝑇𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛 = 15 km / 1/3h= 15 x 3 km = 45 km / h

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To find the distance moved by the car between 8:30 AM and 8:50 AM, subtract the initial odometer reading from the final odometer reading:

Initial odometer reading = 57321.0 km

Final odometer reading = 57336.0 km

Distance moved = Final odometer reading – Initial odometer reading

Distance moved = 57336.0 km – 57321.0 km

Distance moved = 15.0 km

Therefore, the distance moved by the car between 8:30 AM and 8:50 AM is 15.0 kilometers.

To calculate the time taken:

Time taken = Time at 8:50 AM – Time at 8:30 AM

Time taken = 20 minutes (since 8:50 AM – 8:30 AM = 20 minutes)

Now, to calculate the speed of the car in km/min:

Speed = Distance / Time

Speed = 15.0 km / 20 min

Speed = 0.75 km/min

To express the speed in km/h:

Since 1 hour = 60 minutes,

Speed in km/h = Speed in km/min * 60

Speed in km/h = 0.75 km/min * 60

Speed in km/h = 45 km/h

Therefore, the speed of the car during this time period is 0.75 kilometers per minute or 45 kilometers per hour.