Time,Speed and Distances -Astonishing shortcuts

TIME,SPEED AND DISTANCE

Tricks 1: ST=D (remember it as STD calling)

Speed × Time = Distance

From STD method, you can easily derive all the formulas.

Speed = Distance ÷ Time

Time = Distance ÷ Speed

Tricks 2: Speed is inversely proportional to time.

Please understand that, If speed is high then time taken to cover x distance will be less and if speed is slow then time taken to cover the same distance x, will be more.

Speed ∝ (1 / Time)

-distance covered is constant

Tricks 3: To convert km/hr to m/sec and m/sec to km/hr.

We know, km/hr is bigger value and m/sec is smaller so what we do to convert bigger value into smaller?

We divide by a value which has greater denominator than numerator. so to convert km/hr into m/sec we multiply by 5÷18, where 18 (denominator) is greater than 5 (numerator).

x km/hr = x × 5÷18 m/sec

Similarly, To convert m/sec to km/hr, we do the reverse process.

x m/sec = x*(18/5) km/hr

Tricks 4: Average Speed

If a person or object covers a certain distance at x kmph and an equal distance at y kmph, the average speed of the whole journey.

Average speed = 2xy ÷ (x + y)

Tricks 5: Ration of speed

If the ratio of the speed of A and B is a:b,then the ratio of the time taken by them to cover the same distance is 1/a:1/or b:a

Tricks 6: Relative Speed

If two objects are moving in the same direction at v1 m/s and v2 m/s respectively where v1>v2, then their relative speed (v1−v2) m/s.

For Example:

a man, travelling in train can count 21 poles in one minute.If they are known to be 50 meters apart. What is the speed train travelling?

Solution:

Step 1:Find out all the values given in the question and note down.

In this example, we need to find out all the values given in the question.

Number of poles = 21

Distance b/w each pole = 50 meter.

Step 2:  Draw a basic sketch of distance and write values on that.

Draw a sketch, in this example drwaing a sketching don’t benefit much.

Pole 1 |—|—|—|—|—|—|—|—|—|—|—|—|—|—|—|—|—|—|—|—|—|—|—| Pole 21

Step 3: Covert all the values in single unit (either km/h or m/sec)

Distance b/w two pole is 50 meter, convert it to km/h ⇒ 50/1000 ⇒ 1/20

Time taken is 1 minute ⇒ 1/60 hr

Step 4: Try to find all the possible values from given values.

Total Distance: 21 × 1/20 ⇒ 21/20

Step 5: Put all the finding in equation and get the desired answer.

Formula, from tricks 1, ST = D

S (1/60) = 21/20

s= 63 km/hr — Answer

 

A person crosses a 600 m long street in 5 minutes. What is his speed in km per hour?

An aeroplane covers a certain distance at a speed of 240 kmph in 5 hours. To cover the same distance in 1 hours, it must travel at a speed of:

If a person walks at 14 km/hr instead of 10 km/hr, he would have walked 20 km more. The actual distance travelled by him is:

The speed of a train is 90 kmph. What is the distance covered by it in 10 minutes?

4. A car covers a distance of 624 km in 6 ½ hours. Find its speed?

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