Lecture 6.docx - Practice Questions 1 Displacement velocity...

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Practice Questions 1. Displacement, velocity and acceleration curves for a vertical jump. (Vertical Motion only and include the landing. o You have the person standing and there is a displacement in Y The Line represents where the centre of gravity of the body is at each point in time Start and end at the same posture so the centre of gravity is in the same place It goes down when you crouch and that is the lowest part so it’s the lowest point of the centre of gravity Straighten up again and pass the centre of gravity and go past it before they take off because they need to raise their arms Once in the air, they crouch down to absorb it then come back up to standing That’s what displacement is o Now we need to find velocity Anytime it was sloping down it is a negative velocity and anytime sloping up it is positive velocity Way down is negative velocity and way up and even first part after they take off is positive velocity Top of up is the apex and they come down again Eventually hit the ground and that is a negative velocity Then they stand back up again and that is a positive velocity We can find the zero as well Cross at 0 when you change direction of velocity o Going from negative to positive need to go through 0 or vice versa Section is all negative All below 0 But still has a shape o If you look at it closely, initially they are at 0 and then keep going bit by bit and hit a peak velocity then slow o This peak represents the steepest section Gets a downward velocity then a lot then a little then back to 0 If displacement was a straight line of some sort or there are places where velocity change is straight line That is where we have a constant acceleration o Section from takeoff to landing In that region, it is a straight line
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If you have a constant acceleration which you do in the air then you have a straight line for velocity o Acceleration Now just using velocity curve Have negative acceleration to begin with Start at 0 and have a negative acceleration Halfway at the bottom we get a slowing down Slowing down in the negative direction is a positive acceleration Positive slope Acceleration is positive The long negative section is a constant negative acceleration Acceleration due to gravity because we are in the air Continued
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