Question

Cars moving along a straight line at a speed of 54km/hr stop in 5s after the brakes are applied. (a) Find the acceleration, assuming it to be constant. (b) Plot the graph of speed versus time. (c) Using the graph. Find the distance covered by the car after the brakes are applied?

Answer 1

THIS IS NOT SAME BUT VERY SIMILAR QUESTION .. TRY IT BY PUTING 54KMH APART OF 52KMH
.

Firstly, for the first car:
Initial speed, u = 52 km/h2
(We know that 1km=1000m and 1 hour=3600 seconds)
= 

= 14.4 m s-1 (i)

Final speed, v = 0 (As the car stops) (ii)

Time taken, t = 5 s (iii)

Now, for the second car:
Initial speed, u = 34 km/h
(We know that 1km=1000m and 1 hour=3600 seconds) 


= 
= 9.4 m/s (iv)
Final speed, v = 0 (As the car stops) (v)
Time taken, t = 10 s (vi)


In the graph, we will plot time taken in X-axis and speed in the Y-axis. In the graph the sloping point AB is the speed-time graph for the first car and the sloping point CD is the speed-time graph for the second car.



Now we have to find the distance travelled under the graph line AB = Area under triangle OAB

= × base × height

=  × 5 × 14.4

= 36 m (vii)

Now we will find the distance travelled under the line CD = Area under triangle OCD

= × base × height

=  × 10 × 9.4

= 47 m (viii)

Therefore, from (vii) and (viii) it is clear that the second car travels farther as compared to the first after the application of brakes.

Answer 2

Answer:

Initial velocity (u)=54 km/h that is 15 m/s. Time (t)=5 sec. Therefore acceleration is -3.