Projectile Theory Homework: Understanding Velocity and Fall Time

[gamer1319]

Homework Statement

1)A person jumps horizontally from a certain height. If there is no air friction, will his Vh be effected?
2) to calculate his fall time, can you use change in horizontal height = velocityhorizontal
multiplied by time. (time is duration of fall)
3) if one wishes to find the duration of his fall, is the vertical comp of motion just as if he was falling down straight from rest?

Homework Equations

The Attempt at a Solution

1) Yes, it will. The object is moving through the air both horizontally and vertically at the same time, resistance from the air is experienced in both axe.
2) No, you cannot. The duration of falling has no connection whatsoever.
3) Yes, vertical is not connected with horizontal.

PLEASE HELP!

 

[danago]

1) Yes, it will. The object is moving through the air both horizontally and vertically at the same time, resistance from the air is experienced in both axe.

In the original statement you said that there is "no air friction" hence Vh will not change; the only force will be gravity which will act to increase the vertical speed.


If you happened to know the horizontal distance traveled, then you could use it along with the horizontal speed to find the time of flight (the person will only be moving horizontally for as long as he is moving vertically). However, if you did not know the horizontal distance covered, then yes you can treat the vertical motion as if it was an object dropped without a horizontal velocity.

 

[fss]

1)A person jumps horizontally from a certain height. If there is no air friction, will his Vh be effected?

1) Yes, it will. The object is moving through the air both horizontally and vertically at the same time, resistance from the air is experienced in both axe.

The problem states there is no air resistance. Re-evaluate your answer.

2) to calculate his fall time, can you use change in horizontal height = velocityhorizontal multiplied by time. (time is duration of fall)

2) No, you cannot. The duration of falling has no connection whatsoever.

Your wording of this question is exceedingly confusing. Horizontal height? You need to re-think this one too. If the person jumps, is the time it takes to fall from h = h0 to h = 0 the same time you'd use to calculate how far the person travels horizontally? Why or why not?

3) if one wishes to find the duration of his fall, is the vertical comp of motion just as if he was falling down straight from rest?

3) Yes, vertical is not connected with horizontal.

Vertical what? Vertical falling time? Vertical velocity? Vertical acceleration? Part of your problem seems to be that you aren't making these important distinctions. Your answer here is correct; but you didn't seem to use this fact in part (2) of the problem.

 

[gamer1319]

Projectile Help

Moderator's note: two threads merged by Redbelly98

Homework Statement

A person jumps horizontally from a certain height. (Vh = speed)

Q - Can the horizontal distance (traveled AFTER the leap) be calculated as : DistanceHorizontal = VelocityHorizontal * AmountOfTimeHeWasFalling

The Attempt at a Solution

I said NO. The amount of time he was falling bears no relevance to his distance. For example, if a guy jumps 1m horizontally from a 100 m building, his horizontal distance will only be 1m. Using the above formula, his horizontal distance would be much more, which is wrong.

^ is that right?

 

[danago]

The equation is correct.

If he jumps from a height of 100m, ignoring air resistance, he will take about \sqrt{\frac{100}{9.8*0.5}}= 4.5 seconds to hit the ground. If he only travels a 1m horizontally, his horizontal velocity must have been 1/4.5 = 0.22 m/s

 

[gamer1319]

i think you misunderstood the question:

can you figure out his HORIZONTAL DISTANCE traveled after the jump ( he jumped off horizontally) as [DISTANCEHORIZONTAL = VELOCITYHORIZONTAL * (Amount of time that he's freefalling)]

 

[danago]

Yes, you can. There is no acceleration in the horizontal direction (assuming no air resistance), so the equation is valid. The time of flight is the same for both the horizontal and vertical directions -- when the projectile stops moving vertically, it also stops moving horizontally.

Lets consider the example you posted above; however, let's assume that you told me the vertical height (100m) and the initial horizontal velocity (0.22 m/s). From the vertical height, i could calculate the time of 4.5 seconds. I can then calculate the horizontal distance:

D_h=V_ht=(0.22)(4.5)=1 m

 

[Redbelly98]

Due to a forum rule violation, it is necessary to lock this thread.