The shape of a velocity-time graph for constant acceleration is a straight line.
When an object undergoes constant acceleration, it means that its velocity changes by the same amount in equal time intervals. In other words, the object's acceleration remains constant throughout its motion.
On a velocity-time graph, the velocity is plotted on the y-axis, and time is plotted on the x-axis. Since acceleration is the rate of change of velocity, a constant acceleration corresponds to a linear increase or decrease in velocity over time.
If the object is undergoing constant positive acceleration (e.g., a car accelerating forward), the velocity-time graph will show a straight line with a positive slope. The slope represents the rate of change of velocity, which is the constant acceleration.
If the object is undergoing constant negative acceleration (e.g., a car decelerating or moving in the opposite direction), the velocity-time graph will show a straight line with a negative slope. Again, the slope represents the rate of change of velocity, which is the constant negative acceleration.
In both cases, the resulting velocity-time graph will be a straight line, indicating that the velocity changes uniformly over time due to the constant acceleration.