Question

A car is moving with a speed of 90km\h the driver sees a road sign stating that there is a block in the road 1km he applies brake to produce an uniform acceleration of -0.5m\s². find how far before the block the car stops

Answer 1

The man takes 40 sec to cover ( 4 * 10 ) 40 metres. This shows he covers one metre in one sec.

In 2 min 20 sec (140 sec) , he will cover a distance of  140 metres.

Thus he completes  

140

40

= 3.5 rounds in 2 min 20 sec.

Hence it is noticed that he will be at the opposite side from where he started.

Now considering two simple cases.

Case (i)

If the man started at a corner of the square street:

In this case, the man would be diagonally opposite to the place from where he started

Displacement = diagonal of square with side 10 metre.

=   

10

2

+

10

2

−

−

−

−

−

−

−

−

√

=   

100

−

−

−

√

=14.1m

Case (ii)

The man started from the middle of the road.

After the end time, he is in the opposite side of the road.

Hence, the displacement is 10 metre.

 

Answer 2

A car is moving with a speed of 90km/h. The driver sees a road sign stating that there is block in the road in 1km. He applies brake to produce an unifrom acceleration of-0.5m/s2. Find how far before the block the car stops?