Todays concept is called Relative speed

Todays concept is called Relative speedWelcome to the section where everything is related, but only when it comes to speedYou can complete this topic easily in 5 minutes(5 minutes 1 topic, best deal ever! )So far, we were just concerned with one object and its speed, but what if there are two or maybe more objects which are moving at the same time. What do we do then?

We can understand this by knowing their relative speed, which is our concept for today. Lets start now, and in full speed. It is easy to understand relative speed. If you are waiting in a car, you will see another vehicle which is going at 80 km/hr as a blur when it passes by you.But if you are travelling at 60 km/hr, you will see the same vehicle going at 80 km/hr will go idly by you and you might even identify who is driving the car.You can see that the other vehicles speed was the same in both scenarios but since your speed changed, you had two different experiences. This is where the term relative speed comes in.In the first instance since you are at rest, you say that the car was travelling at a relative speed of 80 km/hr. But in the second instance since both of you are travelling in the same direction, you subtract your speed from the other to get the relative speed of the other vehicle. In this case it is (80-60) = 20 km/hr Thus in both instances the speed of the other car did not change but its speed relative to your own speed changed.Now what if the other car was coming towards you, how do you calculate its relative speed then?Well, you just add your speed to the other, which in this case would be (60+80= 140 km/hr.)Think about it, if it was just a blur when you are standing still, it will be lightning fast! if you are travelling towards it.Lets strap ourselves in a sports car and find these relatives and their speeds, shall we?Let us assume you are driving a Ferrari Enzo (I said assume, right) at a speed of 180 km/hr. You look in the side mirror and see a Porsche Carrera GT gaining on you steadily.It must be 100 metres behind you right now. But you find that by the time you travel 900 metres more, it passes you in a hurry. Can you find the relative speed of the Porsche?Let us solve this exercise in stages. First we find the time taken by you to cover 900 metres at a speed of 180 km/hr. As we know Time = distance / speed = 0.9 km / 180 km/hr = 0.005 hrs.Thus it took 0.005 hrs for you to cover 900 metres. But the Porsche took the same time to cover 900 m +100 m = 1 km (as it was 100 m behind you.)Thus its speed = distance / time = 1/ 0.005 = 200 km/hrNow we know the speed of both Ferrari and Porsche. We also know that both were going in the same direction.Hence we deduct the speed to get the relative speed which is (200 180) = 20 km/hrWhat if you had deducted 200 from 180? Well that would give you a negative speed of 20 which is not possible. We can simplify this by putting mod on the equation. Hence |180-200| = 20. Now you dont have to worry about that pestering negative sign. We found out the relative speed when the cars were travelling in the same direction. Is this similar to when two cars are travelling towards each other.New scenario, same cars!You call the Porsche owner and say lets meet up, but the Porsche girl tells you she lives 120 km from you.You suggest that we will just drive towards each other and meet up in between. She agrees. Now assuming she travels at a constant speed of 130 km/hr and you travel at 120 km/hr, can you calculate at what distance you two will meet?We use a simple formula to solve this type of problem, which is Time taken to meet = Distance between them / (relative speed)As distance given is 120 km. and since you are in opposite directions, you add the two speeds to get the relative speeds = 130 + 120 = 250 km/hrUsing the formula, time = distance/ relative speed= 120/250 = 0.48 hrsThus the distance travelled by you in the time = speed * time = 120 * 0.48 = 57.6 kms when you two will meetBut this was about two cars, what about a scenario where some factor actually increases or decreases the speed of the object (like Supermans speed decreases when you put Kryptonite on him.)Lets solve a problem directly and learn as we goA family rented a motorboat and travelled down a river for 90 km with the motorboat showing a speed of 25 km/hr. they read a sign which said the speed of the river was 5 km/hr.While coming back, how much distance will the family cover when they will travel against the current of the river?Since they were traveling with the current of the river first, we have to add the river speed to the boat speed to get the total speed which is (25 + 5) = 30 km/hr. The time taken = Distance / speed = 90/30 = 3 hrs.While coming back, since they are travelling against the current, the total speed = 25-5 = 20 km/hrTherefore the distance travelled = time * speed = 20 * 3 = 60 kmNow you know the concept of upstream and downstream. Can you find the speed of a river if other factors are given. Lets check it outA boat travels 135 km downstream in 1.5 hrs. while going upstream it travels 180 km in 3 hrs. the speed of the motorboat is 75 km/hr. Can you calculate the speed of the river currentLet us find the downstream and upstream speed first.Here, downstream speed = 135/1.5 = 90 km/hr andupstream speed = 180/3 = 60 km/hr

Now the speed: Downstream = boat speed + river speedUpstream = Boat speed river speed.Let river speed be x, henceNow, downstream = 75 + x = 90upstream speed = 75 x = 60Solving for x, we get river speed = 15 km/hr And with that you figured out relative speed. That is awesome! You are more than halfway there!Within no time you would be able to rattle off these concepts in your sleep, while having a dream of you driving a Lamborghini!Lets move on to the next topic.Only 5 minutes of your time is needed, which is approximately the time taken by you to make Maggi and eat it too!Ready for it?Lets Go!