Three more QUICK physics question for Physic Buffs..

[GoldenGuppy]

An airplane is heading due south at a speed of 500 km/h. If a wind begins blowing from the southwest at a speed of 100km/h average, calculate the VELOCITY <magnitude and direction> of the plane relative to the ground... b) how far off course it will be after 10 minutes

a) is 435 km/h

I'm having trouble w/ B though


________



A projectile is fired w/ an initial speed of 75.2 m/s at an angle of 34.5 degrees above hte horizontal axix. Determine A) Maimum Height reached B) the total time in the air C) the total horizonatal distance covered D) the velocity of the projectile after 1.5 seconds


a)92.6 m
b)8.69 seconds
c)538.6 m

I need help w/ D


___________


A projectile is shot from the edge of a cliff 125 m above ground level w/ an initial speed of 105 m/s at an angle of 37.0 degrees with the horizontal. a) Determine the time taken by the projectile to hit point P at ground level. b) Determine the range X of the projectile as measured from the base of the cliff. At the instant just before the projectile hts point P, find c) the Horizontal and vertical components of its velocity d) the magnitude of the velocity and e) the angle made by the velocity vector with the horizontal

a) 14.6 seconds
b)1.224x10^3 meters
c)83.9 and 80 <------ I need an accuracy check on that 80...

I need help w/ D and E


Thanks for any help

 

[Napalm381]

For the airplane one...the original velocity vector was [0, -500]. Now it is [0, -500] + [70.7, 70.7] = [70.7, -429.3]. That's in km/hr. Convert that to km/minute and see how many km away from it's intended point it will be after 10 minutes.

 

[Napalm381]

Second one...the orginal velocity is 75.2[cos 34.5, sin 34.5]. After 1.5 seconds, the x-component will not have changed, while the y component will be equal to 75.2(sin 34.5) + 9.8*1.5. The only external force is gravity, which only affects the y component, changing the velocity by 9.8 m/s.

 

[Napalm381]

Third one...the magnitude of the velocity is just the speed, which is equal to the magnitude of the vector. Assuming you computed part C correctly, this is just (83.5^2+80^2)^0.5.

Part E, the angle is equal to the angle between [1, 0] and [83.9, -80]. The angle between any two vectors can be found as following:
cos(theta)= DotProduct(u,v) / (magnitude(u) * magnitude(v)). Or in words, the dot product of the two vectors divided by the product of the magnitudes. Take the inverse cosine of that and you'll have theta.

 

[DataFly]

1-a) You still need to find the direction of the plane.
1-b) Since you know the velocity it should have, you can calculate where it should be after 10 minutes. You can also calculate where it will actually be after 10 minutes because you know its true velocity. Create a triangle with two sides being the actual distance and direction traveled and the other being the intended distance and direction. You should be able to find the angle between them and can solve for the side opposite the angle. I got ~12km.

2-d) Because you know the initial speed of the projectile and its direction, you can find its horizontal velocity (Vh), which should remain constant, and its initial vertical velocity (Vv) by breaking it apart into its component vectors. Using the equation Vfinal = Vinitial + acceleration * time, plugging in Vv for Vinitial, -9.8m/s^2 for acceleration, and 1.5s for time you can find vertical speed at time=1.5s.

3-d) Make right triangle with the horizontal and vertical velocity as the legs. Using the Pythagorean Theorem, (square the legs, add them, and then take the square root..you know what I mean) find the hypotenouse. This is the magnitude of the final velocity.
3-e) Using the triangle you made in part D, set up the equation tan x = Vv/Vh, and solve for angle x. Remember, because the projectile is heading downward that the angle should be below the horizontal.


I hope that helps.


EDIT: Damn, Napalm beat me to it.

 

[Mday]

i wonder why people help me with my hw problems ;-)

 

[Napalm381]

Mday, I will help you with abstract algebra if you help me with inorganic chemistry.

 

[Gaul]

do people ever do their own hw anymore?

 

[jyrixx]

you're all cheaters!!


(can someone help me with my ... ) darn i couldnt think of anything i need help with
oh well it was almost funny...

 

[GoldenGuppy]

Thanks for all the help guys

 

[DataFly]

No, I am not helping him cheat. If I was I would have simply posted the answers. Teaching him how to solve the problems so he understands the concepts is not the same as spoonfeeding him.


<< Give a man a fish, and he eats for a night. Teach a man to fish, and he eats for life. >>


Or something like that.


GoldenGuppy, you're welcome.