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.