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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facundo3141592 facundo3141592 · Answer 1 · 2021-03-19T01:22:05+01:00

Answer:

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