Solving Long Jump Question: Find Takeoff Speed

[SirMarksAlot]

Homework Statement

A runner jumps at 30 degrees to the ground and covers 8.90 m. What was the takeoff speed?

The Attempt at a Solution

I have no idea where to start...

 

[rl.bhat]

Resolve the velocity into vertical and horizontal components.
What happens to these components with respect to time?

 

[SirMarksAlot]

how would i go about solving the velocity for each component?

 

[rl.bhat]

If v is the velocity what are the vertical and horizontal components?

 

[SirMarksAlot]

honestly, i have no idea

 

[rl.bhat]

Open any textbook. And refer the motion in two dimension.

 

[SirMarksAlot]

but all i have is the angle of the jump and the distance...no time or anything

 

[rl.bhat]

Using proper equation you can find the remaining unknown quantities. Try to find out the equations.

 

[SirMarksAlot]

do u mean these formulas?

Fx = cos A * F1
Fy = sin A * F1

 

[SirMarksAlot]

honestly, I am struggling and have no idea what to do...

 

[rl.bhat]

do u mean these formulas?

Fx = cos A * F1
Fy = sin A * F1

Yes. These are the two components. Only replace F by v for the velocity.
In that x component remains constant, because there is no acceleration in that direction. If t is the time of flight, then x = vcosθ*t.
In the vertical direction, the initial velocity is vsinθ. What is the final velocity when it reaches the maximum height. And what is the time taken to reach the maximum height?

 

[SirMarksAlot]

when u say x = vcosθ*t , what is v? the speed before the jump?

 

[rl.bhat]

No. You have to find out. I have told you to write down all the kinematic equations. Then I will tell you which equation to be used to find the time.

 

[SirMarksAlot]

oh wouldn't the final velocity be 0 when it reaches a maximum height? because he would have stopped moving up?

 

[rl.bhat]

Yes.

 

[SirMarksAlot]

I don't know how to find the time it would take to reach the max height.

 

[rl.bhat]

Why can't you write down all the relevant kinematic equation. In the post submitted to PF, this is the second requirement.. You have not submitted that. Do it first now.