Finding Magnitude of Velocity with Variables

AI Thread Summary
To find the magnitude and direction of the pebble's velocity as it leaves Romeo's hand, the horizontal and vertical components of velocity, Vx and Vy, are crucial. The equations Vx = VCosA and Vy = VSinA are relevant, with the understanding that initial vertical velocity (Vy) should not be zero, as this implies no upward motion. The time to hit the window can be calculated using t = x/Vx, and the vertical distance can be expressed as y = 1/2 gt^2. Clarification is needed on the initial conditions of the pebble's motion to accurately solve for velocity.
RedRumRiots
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Homework Statement


Romeo tosses a pebble at Juliet's window. Before crashing through the window the pebble is moving horizontally, having traveled a horizontal distance x and a vertical distance y. Find the magnitude and direction of the pebble's velocity as it leaves Romeo's hand.


Homework Equations


I know that Vx=VCosA and Vy=SinA.
Also, t=VSinA/g


The Attempt at a Solution


The attempts are pretty much any relevant equations I can find. There's no real math, except I know that the initial Vy is 0. I also figured if the projectile was graphed it would be the right side of the vertex of the parabola. This is why t=VSinA/g. I do not know where to go from here though. I was thinking of using y=VsinA*t-.5g(t)^2. but I really don't know
 
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You know this -

time to hit window, t = x/Vx where Vx is the x velocity

Vy = gt, because Vy=0 at time t ( the sign may be wrong here, Vy is in the opposite direction to g)

y = 1/2 gt^2, distance traveled vertically in time t.

Some manipulation should give what you're looking for.
 
Last edited:
I don't understand this. How can we figure out what t is. I do understand that y = .5gt^2. Just not the rest of it. Any help here would be appreciated!
 
Hi RedRumriots,

RedRumRiots said:

Homework Statement


Romeo tosses a pebble at Juliet's window. Before crashing through the window the pebble is moving horizontally, having traveled a horizontal distance x and a vertical distance y. Find the magnitude and direction of the pebble's velocity as it leaves Romeo's hand.


Homework Equations


I know that Vx=VCosA and Vy=SinA.
Also, t=VSinA/g


The Attempt at a Solution


The attempts are pretty much any relevant equations I can find. There's no real math, except I know that the initial Vy is 0.

Why do you think the Vy=0 initially? You do know that Vy is zero right before the stone hits the window; what does that tell you about that point of the trajectory?

If Vy=0 initially, then this stone would never move upwards.
 
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