Question

147. A car covers 2/3 distance with 60 km/h and 1/3 distance with 20 km/h. Average speed is

Answer 1

Concept:

We know, that speed is expressed by the formula, speed = distance/time

Given:

The car covers a distance of about 2/3 with a speed of about 60 km/hr

The car covers a distance of about 1/3 with a speed of about 20 km/hr

Find:

We need to determine the average speed of the car.

Solution:

Let x be the total distance travelled by car.

We know, speed = distance / time

Therefore, time = speed × distance

Then, t1 time was taken by the car to cover 2/3 distance.

∴ t1 = (2s/3)/60 = s/90 hr

Then, t2 time was taken by the car to cover 1/3 distance

∴ t2 = (s/3)/20 = s/60 hr

Thus, total time, t = t1 + t2

t = s/90 + /60

t = s/36 hr

Therefore, average speed = distance/ time

average speed = s/(s/36) = 36s/s

∴ average speed = 36 km/hr.

Thus, the average speed of the car is 36 km/hr.

#SPJ2

Answer 2

Answer:

60km/h is the required average speed.

Explanation:

Given that, a car covers $\frac{2}{3}$ a distance of 60 km/h

and Cover $\frac{1}{3}$ a distance of 20km/h.

As we know that the formula,

Speed = $\frac{Distance }{Time \ taken}$

Time is taken to cover $\frac{2}{3}$ the distance with a speed 60 km /h = $\frac{Distance}{Speed}$

⇒ Time ($t_1$) = $\frac{\frac{2}{3} }{60}$ = $\frac{1}{90}$ hrs

Now, time taken to cover $\frac{1}{3}$ the distance with a speed 20km/h

Time $(t_2)$ = $\frac{Distance}{Speed}$

⇒ $(t_2)$ = $\frac{\frac{1}{3} }{20}$ = $\frac{1}{60}$ hrs

Total distance travel by car$(d_1 + d_2)$  = $\frac{2}{3} + \frac{1}{3}$ = $\frac{2+ 1}{3} = \frac{3}{3} = 1$km

Total time taken by the car  ($t_1 + t_2$) = $\frac{1}{60} + \frac{1}{60}$ = $\frac{2}{60}$ = $\frac{1}{30}$ h

Now, as we know that,

Average speed = $\frac{Total \ distance}{Total \ time\ taken}$

⇒ Average speed = $\frac{1}{\frac{1}{60} }$ = 60km/h

Hence,  60km/h is the average speed.

#SPJ2