Question

CLASS 9 ...PHYSICS:MOTION
A car starts from rest and moves along the x-axis with constant acceleration 5m/s² for 8 seconds.If it then continuous with constant velocity,what distance will the car cover in 12 seconds since i started from rest ? (ans:320m)

Answer 1

Given:

u = 0, a = $\sf{5\:m/s^{2}}$, t = 8 seconds

We know that:

$\boxed{\sf{v=u+at}}$

Now, substituting the above values, we get:

$\implies$ $\sf{v = 0 + 5 \times 8}$

$\implies$ $\sf{v = 0 + 40}$

$\implies$ $\sf{v = 40 \: m/s}$

Therefore:

Constant velocity = 40 m/s

Now:

Distance covered in the first 8 sec:

$\implies$ $\sf{s = \frac{1}{2} at ^{2}}$

$\implies$ $\sf{s = \frac{1}{2} \times 5 \times 64}$

$\implies$ $\sf{s = 5 \times 32}$

$\implies$ $\sf{s = 160 \: m}$

Now:

Distance covered in the last 4 sec:

$\implies$ $\sf{Speed \times Time}$

$\implies$ $\sf{40 \times 4}$

$\implies$ $\sf{160 \: m}$

So:

Total distance covered in 12 sec:

$\boxed{\sf{160 + 160 = 320 \: m}}$

Therefore:

Answer: 320 m