Question

A car travels with a speed of 30km/h for 30 minutes and then with 40 km/h for 1 hour. Find (i) the total distance travelled by the car ii)Average speed of car.​

Answer 1

distance is equal to speed into time

so distance 1= 30×30/60(converting minutes to hrs) =15 km

distance 2=40×1=40km

total distance is 15+40=55km ans

average speed is total distance/total time=55/1.5 = 36.66 minutes

Hope this helps

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Answer 2

Explanation:

ANSWER:-

(i) To find the Total Distance,

We need to remember the formula

$speed = \frac{distance}{time}$

• And also, maintain the SI units, detailed explanation below.

As we can see, we need to convert the units.

As of first case:-

If I take the final value in Kilometres, then I need to convert 30 minutes in hour.

$30 \: minutes = \frac{1}{2} hr$

Now, calculating distance:-

$distance = speed \times time$

$= \frac{30}{2}$

Final distance as of first case is 15 Km.

Second case:-

Distance = 40×1 ( Units stable)

Distance = 40 km.

Total distance = 40+15

= 55 km/ hour.

(ii) To find the average speed:-

$Av. \: Speed = \frac{total \: Distance}{total \: Time}$

$Av.Speed = \frac{55}{ \frac{3}{2} }$

( 3/2 came after adding 1+1/2)

$= \frac{55 \times 2}{3}$

$= \frac{110}{3}$

Average speed = 36.6 km/ hour.(approx.)

Things to Remember:-

• In general cases only:-
• Always convert the units into SI units.
• SI Unit of speed is m/s
• SI unit of Distance is metre
• SI unit of time is second.
• Now as here majority was in Kilometre per hour, so I chose not to convert it rather keep it simple and converted only one unit above.