A car goes from rest to 30 m/s in 12 s w constant acc. How long does it take the car to go from rest to 15 m/s w the same acc?

Time taken by the car = 6 seconds.

Explanation:

Given:

Case 1:

Initial velocity of the car, = 0

Final velocity of the car, = 30 m/s

Time taken by the car, = 12 sec

Case 2:

Initial velocity of the car, = 0

Final velocity of the car, = 15 m/s

Solution:

Lets find the acceleration in first case:

⇒ acceleration (a) = (final velocity - initial velocity) / time

⇒

⇒

⇒

⇒

Using this acceleration value we can find the time taken in case 2:

⇒ time taken (t2) = (final velocity - initial velocity) / acceleration

⇒

⇒

⇒

⇒

So time taken by the car to go from rest to 15 m/s is 6 seconds.

i think the answer is b

answer: 802.3 kilo joules of energy represents 191.75 kilo calorie of energy.

explanation:

energy released during combustion of one mole methane = 802.3 kilo joules

if 1 kilo joule = 0.239006   kilo calorie

then ,802.3 kilo joule will be = 802.30.239006 kilo calorie

802.3 kilo joule = 191.75 kilo calorie

hence, the energy in kilo calorie is 191.75 kilo calorie.