A ball is thrown vertically upwards from the hand and lands back onto the hand. It is important to note that once the ball leaves the hand, the resultant force acting on the ball is only its weight! And it is acting downwards throughout the motion.
Velocity-Time Graph
Displacement-Time Graph
Key points to note when sketching the v-t graph:
1) Fixing the direction up to be positive (can be down as positive if you want)
2) At t = 0s, the initial velocity of the ball is maximum.
3) As it goes up vertically, due to the weight acting downwards, the ball decreases in speed (decelerates)
4) At the highest point, the ball is momentarily at rest (v =0m/s)
5) On the way down, due to the weight of the ball acting downward, the ball accelerates downwards.
April 1, 2016 at 1:42 AM
Why the velocity of the ball is negative when it accelerates downwards ?
April 2, 2016 at 10:41 AM
Velocity is a vector quantity. So direction is important. As up is set as positive, when the ball is thrown up the velocity decreases. It is positive velocity as it is moving upwards. When it is falling downwards, the velocity increases but it’s negative, indicating that the speed is going faster but in the opposite direction. Negative velocity just means direction is opposite. Hope this helps
January 17, 2019 at 8:16 PM
How comes that the acceleration in upward and downward movement is negative
January 17, 2019 at 8:39 PM
Because we fixed up as positive. As velocity decreases as it goes up so it is deceleration (negative acceleration). But as it is coming down, the direction is opposite to just now. Thought it’s speed increases as it comes down, due to moving in opposite direction, the acceration is negative
November 24, 2016 at 1:26 PM
is acceleration negative throughout the motion?
November 24, 2016 at 2:36 PM
Yes. If you set upwards direction as positive
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July 2, 2017 at 9:29 AM
I like this answer
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