hooolahoop

i believe these are the questions.

hawkraven

These are the old questions o.O

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Jodar

^ Yeah those are the old questions

I need more maths qns to keep my mind active! I'm so dumb i left all my assessment books for nearly every subjects under my table in school. Now nothing to do tmr.. $#&@$.. =.=

hooolahoop

hmmm. then i have no idea. or he already solved them. *shrugs*

hawkraven

Nicely done. XD
Have a happy holiday then.

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Jodar

Yeah =.=

Nvm la, slack through the holidays lol.. =.= Shld take a rest or something

enirtep

qns 1b, sketch a velocity-time graph of the motion of the ball from the moment it is thrown to the moment it hits the ground.

i dont really understand, when the strone is thrown upwards, i tot the speed goes from fast to slow (when its at the top), and fast again when its reaching the ground. but why the ans sheet shows the velocity starts from 20 then goes all the way to negative? grr, i hate this chapter

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hawkraven

Velocity is not equal to speed.

Velocity is displacement over time. Not distance over time.

Displacement, in Newtonian mechanics, specifies the position of a point in reference to an origin or to a previous position. In simple terms, it is the difference between the initial position and the final position of an object.

On the graph, when the stone is thrown, is has positive displacement/time as the question states that upward direction is positive. It's speed decreases by 20ms^-1 at 2 seconds, due to gravitational force, and heads downwards. If upwards = positive, downwards = negative. Therefore, the line intercepts the x-axis at 2 seconds (assuming no air resistance), and the velocity reaches negative value. Then, as the stone accelerates downwards, it moves down more swiftly per second, causing a higher negative displacement/time value. When it hits the ground, it no longer moves, and is not displaced downwards, therefore it spikes back up to 0 displacement/second.

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enirtep

ok now i undersatnd the part about the negative value. but if the stone goes upwards, the graph should be increasing, right? because when you throw a stone upwards, it moves from bottom to the top, so during this time, shouldnt the graph be drawn in a way that it increases from 20 up to more than 20, then goes all the way down to negative when it falls from the top back to the bottom?

sorry im abit confused here

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hawkraven

Gravity slows it. Thus, the rate of displacement decreases, but as the value is still positive, it indicates that the stone is still moving upwards.

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enirtep

ORH!! YES OKAY THANKS!!

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RelicDemon12