B. Acceleration. Acceleration is the cars increase in speed, while deceleration is the decrease in speed. Speed is how fast it's going. :) hope this helps
If there are no dissipative forces acting on the string, than the <em>principle of conservation of energy</em> holds.
When the string is relaxed, it has zero elastic potential energy
If we were strech the she spring, we would increase it's potential energy. After releasing the spring, when it's relaxed again, all potential energy will have been converted into kinetic energy.
Therefore, the elastic potential energy of the stretched spring should be equal to the amount of kinetic energy when it's relaxed
We have equation of motion v = u + at
Where v = final velocity, u = initial velocity, a = acceleration, and t = time
In this case car is travelling in -x direction
Velocity of car = displacement / time
Since displacement value is increasing in negative x axis it's initial velocity is negative
And it's final velocity is zero since it comes to rest, and time is also positive
So, v= u+ at => 0 = -u + at
So, a = u/t
Which is positive and along positive X - direction
