Solve Velocity 2D Question: Find Initial Velocity

[s4116792]

Homework Statement

If a long jumper at the top of his trajectory is moving at 6.5 m/s (horizontally) and his centre of mass is 1.1m abover where it was when he launched into the jump, how fast must he have been moving when he launched?

Homework Equations

Vx = Vox + ax*t

The Attempt at a Solution

In all texts i look at they say that the initial velocity should be the same as final velocity in the x-axis but that isn't the correct answer for the question in the text.

Thanks for any help.

 

[Nick89]

Ask yourself this:

Is there a force in the horizontal direction that could cause an acceleration or deceleration on the jumper?

If yes: A force is exerted on the jumper in the horizontal direction thus giving him an acceleration (either forward or backward) thus changing the speed.

If no: No force is exerted on the jumper in the horizontal direction, so the acceleratoin in the horizontal direction is 0, so the horizontal speed does not change.