Solving Velocity Problem: Find the Start Velocity !

  • Thread starter martine80
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In summary, the conversation discusses solving for the starting velocity of an object thrown up a slope at an angle of 60 degrees from the horizontal plane. By using equations for velocity and distance, the speaker is able to determine the starting velocity of 23.8 m/s. However, there is confusion over the angle calculation, which is found to be 28.28 degrees instead of the expected 15 degrees. The conversation also mentions the use of trigonometry and the equation for projectile motion in solving the problem.
  • #1
martine80
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velocity ! HELP

1:you have a lope with an angle of 15 degrees from the horizontal plane. You throw an object with an angle of 60 degrees from the horizontal plane up the slope and the object hits the ground 25m from the starting point. . What is start velocity?

This is what I’ve done:

Y = 25m *sin(15)=6,47m
X= 25m*cos(15)=24,15m
V0y=sqrt(2*g*y)=11,26m/s
.t= voy/g=1,15
V0x=x/t=21m/s
This gives me this result
V0= sqrt(v0x^2+voy^2)=23,8 m/s

But when I check the answere I get the wrong angle?

Tan(ß)=v0y/v0x -> ß=28,28

What am I doing wrong ?:cry:
 
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  • #2
The distance in the x direction equals 25 m, perhaps?
 
  • #3
radou said:
The distance in the x direction equals 25 m, perhaps?

its a slope , why 25 m?
 
  • #4
"t= voy/g=1,15" ?

What is that?

*Wrong comment
 
Last edited:
  • #5
JK423 said:
"t= voy/g=1,15" ?

What is that?

from the equation vy= v0y-gt, I find the time it takes : 1,15 s
vy= 0 when it hits the grownd
 
  • #6
:uhh: :cry:
 
  • #7
"vy= 0 when it hits the grownd"

No, it doesn't.
 
  • #8
martine80 said:
its a slope , why 25 m?

So, it's 25 m along the slope?
 
  • #9
ive solved it, by using
v0x= v0 *cos(60)
v0y=v0 *sin(60)
x= cos(15) *25
y= sin(15)*25
and used :
y=v0y*t-1/2(gt^2)
 
  • #10
ive solved it, by using
v0x= v0 *cos(60)
v0y=v0 *sin(60)
x= cos(15) *25
y= sin(15)*25
and used :
y=v0y*t-1/2(gt^2)

;)
 

1. What is the formula for calculating velocity?

The formula for calculating velocity is velocity = displacement / time.

2. How do I find the start velocity?

To find the start velocity, you will need to know the displacement and time of the object and plug them into the velocity formula. The start velocity will be the initial velocity of the object at the beginning of its motion.

3. Can I use the same formula for all types of motion?

Yes, the formula for velocity can be used for all types of motion, as long as the displacement and time are known.

4. What units should I use for velocity?

The standard units for velocity are meters per second (m/s) or kilometers per hour (km/h). However, you can use any unit of distance and time as long as they are consistent (i.e. both in meters and seconds or both in miles and hours).

5. Is velocity the same as speed?

No, velocity and speed are not the same. Velocity is a vector quantity that takes into account the direction of an object's motion, while speed is a scalar quantity that only measures how fast an object is moving regardless of direction.

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