Projectile Motion Question (physics 101)

  • Thread starter cheese89
  • Start date
  • #1
1
0

Homework Statement



A projectile is shot from the edge of a cliff 125 m above ground level with an initial speed of 65.0 m/s at an angle of 37 degrrees with the horizontal. Find the horizontal and vertical components of its velocity at the instant just before the projectile hits point P (the ground).

Homework Equations



Vxo = Vo cos 37
Vyo = Vo sin 37
Vy = Vyo - gt ...????

The Attempt at a Solution



The answer is given in the back of the book. Plugging in the initial velocity in the first equation gives the correct answer (which I expected), but the answer I acheive for Vyo should be negative and I haven't yet acheived that. I tried to plug the answer I got for Vyo (the positive one) into the equation Vy = Vyo - gt, but still did not get the right answer. I'm truly grasping at straws here.
 

Answers and Replies

  • #2
116
0
You can use Vy = Vyo - gt to find the vertical component, but must first find the time at which the projectile reaches P. To do this, you use the equation for the y-coordinate as a function of time.
 
  • #3
tiny-tim
Science Advisor
Homework Helper
25,836
251
Vxo = Vo cos 37
Vyo = Vo sin 37
Vy = Vyo - gt ...????

Plugging in the initial velocity in the first equation gives the correct answer (which I expected), but the answer I acheive for Vyo should be negative and I haven't yet acheived that. I tried to plug the answer I got for Vyo (the positive one) into the equation Vy = Vyo - gt, but still did not get the right answer. I'm truly grasping at straws here.

Hi cheese89! :smile:

I don't understand how you got any result for Vy from Vy = Vyo - gt … :confused:

you don't know what t is.

Hint: you haven't used y = 125 yet, have you? :wink:
 
  • #4
580
0

Homework Statement



A projectile is shot from the edge of a cliff 125 m above ground level with an initial speed of 65.0 m/s at an angle of 37 degrrees with the horizontal. Find the horizontal and vertical components of its velocity at the instant just before the projectile hits point P (the ground).

Homework Equations



Vxo = Vo cos 37
Vyo = Vo sin 37
Vy = Vyo - gt ...????

The Attempt at a Solution



The answer is given in the back of the book. Plugging in the initial velocity in the first equation gives the correct answer (which I expected), but the answer I acheive for Vyo should be negative and I haven't yet acheived that. I tried to plug the answer I got for Vyo (the positive one) into the equation Vy = Vyo - gt, but still did not get the right answer. I'm truly grasping at straws here.


Its an oral question dear. Just think will the boy acclerate in x direction. If it does, vertical component will change otherwise not. For the y direction, whatever you throw come down with same speed.
 
  • #5
42
0
For this problem you should check your constant acceleration formulas. The Acceleration in this case is a constant -9.8m/s^2(gravity). And there is no acceleration in the x direction. The velocity would be v=Vo+at. where v= final velocity, Vo= initial velocity, a=acceleration, and t= time. Look at the information given to you in the problem and consult some of the other formulas. You have a displacement of 125m, a Vo, the acceleration, the angle. all you need is the time it took to get to the ground and you will have your answer =)
 
  • #6
tiny-tim
Science Advisor
Homework Helper
25,836
251
whatever you throw come down with same speed.

Hi ritwik06! :smile:

That only applies when we throw from the ground … this is from a 125 m cliff. :wink:
 
  • #7
73
0
you have to find time first using the formula Y = vt + 1/2 g t^2
 
  • #8
580
0
Hi ritwik06! :smile:

That only applies when we throw from the ground … this is from a 125 m cliff. :wink:

I know. I thought cheese was working for that interval as well.
 

Related Threads on Projectile Motion Question (physics 101)

  • Last Post
Replies
10
Views
843
  • Last Post
Replies
8
Views
3K
  • Last Post
Replies
4
Views
9K
Replies
4
Views
13K
Replies
19
Views
6K
Replies
3
Views
2K
Replies
4
Views
7K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
5
Views
602
  • Last Post
Replies
8
Views
851
Top