Finding total flight time of a projectile. Please help

In summary, the problem involves finding the total time that a baseball thrown vertically at a speed of 3m/s has been in flight when it has traveled a distance of 50cm. The correct approach is to find the maximum height that the baseball reaches by setting the final velocity to 0 and then calculating the time it takes to reach this height. This time is then added to the time it takes for the baseball to fall back down to the ground, giving a total time of 0.398 seconds, as stated in the answer manual.
  • #1
Ilovepysics
14
0

Homework Statement



A baseball thrown vertically with a speed of 3m/s. Find the total time that the ball has been in flight when it had traveled 50cm.

Homework Equations



vf=vi + at
d= 1/2at^2


The Attempt at a Solution



Found t.
vf=vi +at
vf=3
vi=0
a=~10
Found t= .3 secs

Found d
d=1/2 + at^2
d=4.5m

Added 4.5m to .5m =5m

Plugged in total distance 5m into d=1/2 + at^2
Found t= 1

Added 1+.3 to get total time of 1.3 secs.

The answer in the manual is 0.398 sec.
I am way off can someone please help. Thanks!
 
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  • #2
Ilovepysics said:
d= 1/2at^2

above equation is not always correct.
 
  • #3
grzz what do you mean?

Is there another equation I should be using? or perhaps another approach. I am not sure where I went wrong.
 
  • #4
The equation that I quoted from your post is only correct to use if the initial speed is 0. This is not the case in your problem.
 
  • #5
I also tried using d=vit + 1/2at^2 plugging in 3m/s for vi but I also calculated a wrong answer for t. So I am not sure what equation to use.
 
  • #6
Use the constant acceleration equations. One in particular will allow you to find the final velocity at S = 0.5m, then you can use that to calculate other values e.g time.
 
  • #7
TaxOnFear-
I tried using vf^2 =vi^2 + 2ad to find vf. I got sqroot of 19 for vf and then plugged it into vf=vi+ at to solve for t I got t=.135 sec... still the wrong answer according to the answer manual.
 
  • #8
Ilovepysics said:
TaxOnFear-
I tried using vf^2 =vi^2 + 2ad to find vf. I got sqroot of 19 for vf and then plugged it into vf=vi+ at to solve for t I got t=.135 sec... still the wrong answer according to the answer manual.

You are assuming the projectile has not reached the peak point by this statement. Try breaking the problem down into two sections: one where the projectile is launched up, and the other where the projectile is falling down. Most of the numbers will look the same, but the time in the air will add up.
 
  • #9
I am really confused. I am starting to think there is an error in the answer manual. I have tried all motion equations possible. I assumed it reached peak and used vf=3m/s -- that didnt work. I tried vi=3m/-- that didnt work. I tried d= 1/2at^2 that didnt work either.

Was my initial attempt at a solution (above) completely wrong?? Can someone tell me where I am going wrong. I've tried looking at it from all angles..please help
 
  • #10
Better follow the advice of 'physicsvalk'.

The 50cm may mean the total distance going up AND some distance going down.

Hence try to find the MAXIMUM height it can travel. Of course in finding this you have to put the final velocity equal to 0.

Then find the time to reach this max height and continue from there.
 

FAQ: Finding total flight time of a projectile. Please help

How do you calculate the total flight time of a projectile?

The total flight time of a projectile can be calculated using the equation t = 2v*sinθ/g, where t is the total flight time, v is the initial velocity of the projectile, θ is the angle of launch, and g is the acceleration due to gravity.

What factors affect the total flight time of a projectile?

The total flight time of a projectile is affected by factors such as the initial velocity of the projectile, the angle of launch, air resistance, and the local gravitational force.

How does air resistance impact the total flight time of a projectile?

Air resistance can decrease the total flight time of a projectile by slowing it down as it travels through the air. This is because air resistance creates a force that acts in the opposite direction of the projectile's motion, causing it to lose speed and fall to the ground sooner.

Can the total flight time of a projectile be longer than the calculated value?

Yes, the total flight time of a projectile can be longer than the calculated value due to factors such as wind gusts, air turbulence, and changes in air density. These factors can affect the projectile's trajectory and cause it to stay in the air for a longer period of time.

How does the total flight time of a projectile change with different angles of launch?

The total flight time of a projectile increases as the angle of launch decreases. This is because a lower angle of launch results in a longer horizontal distance for the projectile to travel, leading to a longer flight time. However, if the angle of launch is too low, the projectile may not reach its desired target.

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