Question

a car travel 54 km per hour for first 20 sec, 36 km per hour for next 30 sec and finally 18 km per hour next 10 second find its average speed ?

Answer 1

Now Total Distance = 300 + 300 + 50 = 650 m
Total time = 20 + 30 + 10 = 60 s
Average Speed = 650/60 = 65/6 m/

Answer 2

Hey there!

Formula used:

• Distance = speed * time

• Speed ( in 1 km/h) = 5 /18 (in 1 m/s)

Distance covered when car travels at 54 km/h for first 20 s:

Speed = 54 km / h

           = 54 *( 5/18) m/s

           = 15 m/s

Distance (d₁) = speed * time

                    = 15 * 20 = 300 m

Distance covered when car travels at 36 km/h for  30 s:

S = 36 km/h = 36 * (5/18) m / s  = 10 m/s

d₂ = v * t = 10 * 30 = 300 m

Distance covered when car travels at 18 km/h for  10 s:

S = 18 km/h = 18*(5/18) m/s = 5 m/s

d₃ = v * t = 5 * 10 = 50 m

Average speed = Total distance(d₁ + d₂ + d₃) / Total time

                           = (300 + 300 + 50) m / (20 + 30 + 10) s

                           = (650 m) / 60 s

                           = 10.83 m/s  (←Answer)

Good day!