Projectile race track physics help

1. Mar 2, 2013

Sam Fred

1. The problem statement, all variables and given/known data
The Track for this racing event was designed so that riders jump off the slope at 30°, from a
height of 1m. During a race it was observed that the rider shown in Fig. 2 remained in mid air for
1s. Determine,
1) the speed at which he was traveling off the slope, ( 2points)
2) the horizontal distance he travels before striking the ground, (2points)
3) the maximum height above the ground he attains (3points)

2. Relevant equations
v=vi + at
y=yi + vi t + 0.5 a t^2

3. The attempt at a solution
in the attachment .

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2. Mar 2, 2013

BruceW

Re: Projectile

hey man, welcome to physicsforums! When they say he remained in mid-air for 1 second, I think this means that he was airborne (not touching ground) for 1 second. Not that he was half-way through his jump at 1 second.

3. Mar 2, 2013

Sam Fred

Re: Projectile

aha ... thanks man ... but how would i know the speed off he slope ???
Do i repeat the same steps with substituting t = 0.5 sec

4. Mar 2, 2013

BruceW

Re: Projectile

No. That would work if his jump started and finished at the same height. But in this problem, it doesn't, because he starts the jump at 1m height, and finishes the jump at zero metres. So at t=0.5 sec, he is not at the highest part of the jump (he has already gone past that point). So the time when he has zero velocity will be some value, which is greater than 0.5 seconds.

You can use this equation you wrote: y=yi + vi t + 0.5 a t^2 (also, remember that vi needs to be the vertical component of initial velocity). You know the total change in height and you know the change in time, so you can simply solve for vi