When you stretch the elastic and then let go, the shape of the velocity-time graph for the toy car would not be a decreasing acceleration graph. Instead, it would be a sinusoidal or oscillating graph.
Here's why:
When you release the toy car attached to the stretched elastic, the elastic exerts a restoring force on the car. This force is directed towards the equilibrium position, causing the car to accelerate in the opposite direction to its motion. As the car moves in the opposite direction, the restoring force decreases, and the car's acceleration decreases as well.
At the equilibrium position, the car momentarily stops, and the elastic exerts its maximum restoring force, changing the car's direction. The car then accelerates in the opposite direction again, and the process repeats.
This back-and-forth motion creates a periodic pattern, resulting in a sinusoidal velocity-time graph. The graph would show the car's velocity increasing in the negative direction, reaching a maximum negative velocity at the equilibrium position, and then decreasing back to zero. The car then continues to move in the positive direction, with the velocity increasing, reaching a maximum positive velocity, and then decreasing back to zero. This pattern repeats as long as the oscillations continue.
So, in summary, the shape of the velocity-time graph for the toy car attached to a stretched elastic would be a sinusoidal or oscillating graph, representing the back-and-forth motion of the car due to the restoring force of the elastic.