Physics 3.5.4b - Projectile Practice Problem 2

Practice Problem on Projectile Motion.

[FachrinabilPF]

based on your all videos about projectile motion. I realised that you put either vertical/horizontal first on your working is because it depends on the time. If there is a time in the question, you would firstly use horizontal, vice versa. 

[derekowens]

@DeanNickChase If you look closely you can see in the diagram that it is a stick horse, ridden by a stick figure. Stick horses (and stick figures) are two-dimensional, so they are very thin and extremely lightweight. This gives the horse a tremendous power-to-weight ratio, allowing him to make the jump that a big fat three-dimensional horse could not make.

[RobbyBoy]

100m??!!!! I need to get me that horsey!!!

[lindseyhughes]

thank you so much for this! it's so confusing when my teacher does it but you explain it so well!

[tutstorial]

well here's another approach:

let T = total time (start to peak, peak to...)
T = 5s.
R = 100m.
¢ = angle

since T = 2Voy/g

T = 2Vosin(¢)/g
Vo = gT/2sin(¢) eq1.
Vo = (9.81)(5)/2sin(¢)

x = Voxt eq2
100 = Vocos(¢)(5)
Vo = 100/5cos(¢)


equate e1 & eq 2

9.81(5)/2sin(¢) = 100/(5cos(¢))

sin(¢)/cos(¢) = 5(5)(9.81)/2(100)

tan(¢) = {(5)(5)(9.81)/2(100)}

¢ = 50.81°

substituting ¢ to either eq1 or eq.2

Vo = 31.6 m/s

[omersohail]

If it wasn't for your videos, I would've never grasped the whole idea about projectile motion. You don't know how much help your videos have been to me! I am highly in debt and grateful! Thank You So much and Keep up the Enlightenment!

[babblingmonster]

Its really saddening to see the view count of such a magnificent video...

[derekowens]

@getrichquickideas Thinking from the start to the peak, which is only half of the flight, gives you a result of 2.5 seconds. This is half the total time, so the total time is five seconds.

[remargonzaga]

i'm sorry. but, shouldn't be the initial velocity for x Vocos(theta)? thus, Vo=100m/(5s cos(theta))?

[derekowens]

@jkoscak I prefer m/s, although m s^-1 is mathematically equivalent, and can fit neatly on one line when typing. I think the algebra is more clear, though, with it written as a fraction.

[bloodisfuel]

hey there, I really appreciate your video. but at 3:25 I did not really understand much. Why would you make the time 2.5s? I know that at 2.5s that's when farmer bob and his horse reached maximum height, but why would you do that? Is there another way to get the initial vertical velocity here? thanks

[derekowens]

@H2daH acceleration is zero horizontally. This is always the case for projectiles because gravity always pulls down, and never exerts any force horizontally.

[Rittiuu]

Because v zero is from theta angle so vx will v cos thata I think you made mistake

[DaTurdburglar]

Thanks for the vids! They really helped me alot. :D

[abridgetool]

The problem is quite old.
So the video is.

[rubiksmaster]

The only reason I'm watching this is because it's a physics homework assignment.

[jensons]

the lesson here is clear. on my channel is a projectile motion demo that you can watch. it's actually a program that you can download from softpedia

[Gsmstfreshie]

what if it asks for the landing velocity? would that just be the horizontal velocity, which is 20m/s?

please answer my question, thank you!

[mickyadams]

why dont you use 1/2 as often found in the formula 1/2at squared. When you calculate V zero

[getrichquickideas]

Why is the time for horizontal (5sec) different from you time for the verticle (2.5 sec) ?