Solving a Long Jump Problem: Find Takeoff Speed & Increase Jump Distance

[jonnyboy261]

hey guys imm new here
i got a question in my book i can't figure out
it says:
an athlete executing a long jump leaves the ground at a 30 degree angle and travels
7.80m (a) what was the takeoff speed? (b) if this speed were increased just 5.0 % how much longer would the jump be?

anyone kno how to do this
i tried using the kinematic equations but ther isn't enuf info
please help if u know the answer.
thanks a lot !

 

[suspenc3]

Start out by splitting the problem up into 2 parts: Horizontal motion & Vertical motion. From here, you will have 2 equations with 2 unknowns.

 

[jonnyboy261]

i know to do that.. but i still don't get how u can use the equations when u only have the horizontal displacement of 7.80 m ? how do i use the 30 degree angle to find anything?

 

[tyco05]

You can calculate the time of flight.

If you have a horizontal displacement of 7.8 metres you can use symmetry to find where the highest point is - this is also half way through the flight.

The vertical velocity here is zero.

The 30 degree angle let's you split the flight into its horizontal and vertical components.

 

[jonnyboy261]

ok so i plugged 3.9 m and 0m/s into the displacement equation so it makes t=.892s
and then i found out Vi for vertical is 8.74 m/s
then i used SOH to find the hyponuse to be equal to 17.48 by dividing 8.74 by sin30
is this the right answer?

 

[suspenc3]

Why did you use 0m/s?