Question

Can someone please explain to me when an object is being thrown downward, what does the velocity versus time graph shown? will the acceration be negative or constant?

Answer 1

Since the acceleration 'g' is only due to the gravitational force whose magnitude is 9.8 m/s², the graph will be a straight line as dictated by the given euation of motion,

(its like an equation of straight line with slope 'a' and intercept 'u')

Here, v = final velocity of the object

u = initial velocity of the object

a = acceleration due to gravity

t = time taken by the object to reach from velocity 'u' to 'v'

Suppose, you through something downwards with a speed of 10 m/s, then

u = - 10 m/s

a = -g = - 9.8 m/s²

For the duration of 10 seconds, the velocity-time graph will look like this :

The magnitude of acceleration will always be constant. It will be negative if you are taking upward direction as positive direction and it will be positive if you are taking your positive axis in the downward direction.

In the case of throwing something in downward direction, the acceleration due to gravity is also in the downward direction, so the speed of the object will increase with time.