Answer to Question #140715 in Mechanics | Relativity for anna matic

Question

A person drives back and forth. They start 20 meters away from you at a pace of 10 m/s for 3 seconds, then stand still for 2 seconds, then drive back towards you at a pace of 20 m/s for 3 seconds.

Answer 1

As here question is incomplete, so i am assuming that we have to find the total time to cover 20 reach to the person.

In the first move, person is moving away, so distance move $=10\times 3= 30m$

Distance covered in the return journey$=20\times3=60 m$

So, in the first move, net distance covered $=(60-30)m=30m$

So, again he will move in forward direction, so time taken to cover 30 m at 20m/sec speed $=\frac{30}{20}s =1.5 sec$

Hence total time taken to reach to the person who is standing$=5+1.5 = 6.5 s$