Two bodies A and B are approaching towards each other with speed 10 m/s and 54 km/hr. If the direction of motion of A is taken positive, then what is the relative velocity of B w.r.t. A?

Here,

 V e l o c i t y space o f space b o d y space A comma space stack straight v subscript straight A with rightwards arrow on top space equals space 10 straight m divided by straight s
V e l o c i t y space o f space b o d y space B comma space stack straight v subscript straight B with rightwards arrow on top space equals space minus 54 space km divided by hr space equals space minus 15 straight m divided by straight s
 

∴       

Relative velocity is given by, 

space stack straight v subscript straight r with rightwards arrow on top equals stack straight v subscript straight B with rightwards arrow on top space minus space stack straight v subscript straight A with rightwards arrow on top space equals space minus 15 minus 10 equals negative 25 straight m divided by straight s 

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A car is going due north with velocity 25m/s and a jeep is following the car with speed 90km/h. What is the relative velocity of the car w.r.t. jeep? 

Relative velocity of the car w.r.to jeep is 0. 
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When the magnitude of relative velocity is equal to the difference of the magnitude of the velocities of two bodies?


When the two bodies are moving in same direction along a straight line, then the magnitude of relative velocity is equal to the difference of the magnitude of the velocities of two bodies.
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Rain is falling vertically downward. A man is going in the rain. Which side of the man will get wet?

The rain is falling vertically downwards but the man is in motion. As the man is moving forward, the probability of him getting wet is more. The man will escape the rainfalls falling in sides but, will be hit in the front. 
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Two trains travelling on the same track are approaching each other with the equal speed of 40 m/s. The drivers of the train begin to deaccelerate simultaneously when just 2.0 km apart. Assuming deacceleration to be uniform and equal, the value of the deacceleration to barely avoid collision should be? 


We have, 

Initial speed, u = 40 m/s 

Distance to be covered by each train before rest, s = 1000 m 

Acceleration, a = ? 

Using the relation, 

                  v2 = u2 + 2as

We have, 

straight a space equals space fraction numerator left parenthesis straight v squared space minus space straight u squared right parenthesis over denominator 2 straight s end fraction space
space space space equals space fraction numerator 0 space minus space left parenthesis 40 right parenthesis squared over denominator 2 space straight x space 1000 end fraction space

space space space equals space 0.8 space straight m divided by straight s squared
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