Question

A driver starts from rest on a straight test track that has markers every 0.14 km. The driver presses on the accelerator and for the entire period of the test holds the car at constant acceleration. The car passes the 0.14 km post at 8.0 s after starting the test.
(a) What was the car's acceleration?
(b) What was the car's speed as it passed the 0.14 km post?

Answer 1

Answer:

(A) Constant acceleration will be $a=1.479m/sec^2$

(B) Velocity of the car when it passes 0.14 km is 20.349 m/sec

Explanation:

It is given that driver starts from rest so initial velocity of the driver u = 0 m/sec

Distance traveled s = 0.14 km = 140 m

Time taken to cross 0.14 km is 8 sec

So time taken t = 8 sec

(A) From second equation of motion $s=ut+\frac{1}{2}at^2$

So $140=0\times 8+\frac{1}{2}\times a\times 8^2$

$a=1.479m/sec^2$

(B) From third equation of motion

$v^2=u^2+2as$

$v^2=0^2+2\times 1.479\times 140$

$v^2=414.12$

v = 20.349 m/sec

So speed of the car when it passed 0.14 km is 20.349 m/sec