a)Hari drove for 2 hours at a speed of 60km/h and next3 hours at a speed of 70km/h. Calculatehis average speed for the whole journey.b)A police car drives with a constant speed of 70km/h. How long it will take to cover a distance of 135 km? Express the speed in m/s
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Ответ:
Remember the relation:
Speed*Time = Distance.
Then first let's find the total distance that Hari drove.
First, he droves 2 hours at 60km/h, then the total distance traveled is:
Distance = 2h*60km/h = 120km
Then he droves 3 hours at 70km/h
The distance here is:
Distance = 3*70km/h = 210km
The total distance traveled is 120km + 210km = 330km
The total time of the travel is 2 hours + 3 hours = 5 hours.
The average speed is calculated as:
Av speed = (total distance)/(total time)
Av speed = (330km)/(5 h) = 66km/h
The average speed is 66km/h.
b) We know that the speed is 70km/h, but we want to write this in m/s.
Then we first know that 1 km = 1000m
then:
1 = (1000m/1km)
Then 70km/h = 70 km/h*(1000m/1km) = (70*1000) m/h = 70,000 m/h
Now we know that 1h = 3600 seconds, then:
1 = (1h/3600s)
So we can write:
70,000 m/h = (70,000 m/h)* (1h/3600s) = 70,000/3600 m/s = 0.019 m/s
and the distance is 135 km
Again, we can rewrite this as:
135km = 135km*(1000m/1km) = 135,000m
Then we want to solve:
(0.019m/s)*time = 135,000 m
We want to solve this for the time, then we get:
time = (135,000m)/(0.019m/s) = 7,105,263.2 seconds = 1.93 hours
Ответ:
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Explanation: