How Do You Calculate Initial Velocity and Displacement of a Thrown Stone?

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Homework Help Overview

The discussion revolves around a physics problem involving the motion of a stone thrown from a cliff, focusing on calculating the initial velocity and displacement. The stone is thrown from a height of 80 meters and lands 60 meters away from the cliff.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the application of kinematic equations in both the horizontal and vertical directions. Questions are raised about the direction of gravity and the nature of the velocity in the x-direction. There is also a mention of the angle of throw being perpendicular to the ground.

Discussion Status

Some participants have provided insights into the known variables and the equations needed to approach the problem. There is a focus on finding time using the vertical motion equations and then applying that to the horizontal motion to determine the initial velocity. However, the discussion remains open-ended with no explicit consensus reached.

Contextual Notes

Participants note the absence of the angle of throw and the need to consider the effects of gravity acting in the vertical direction. There is also mention of the need to find the time taken to reach a specific velocity, indicating further complexity in the problem.

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A stone (taken as a point mass) is thrown from a cliff of height H = 80m perpendicular to the ground. It falls L = 60m away from the cliff. What is the initial velocity V with which the stone is thrown?

Obviously we have to deduce the formula for velocity using kinematic equations w/ respect to H and L. Help will be very appreciated. Thank you.
 
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siddharthmishra19 said:
A stone (taken as a point mass) is thrown from a cliff of height H = 80m perpendicular to the ground. It falls L = 60m away from the cliff. What is the initial velocity V with which the stone is thrown?

Obviously we have to deduce the formula for velocity using kinematic equations w/ respect to H and L. Help will be very appreciated. Thank you.

Think of the equations of motion for both the x and y direction. In which direction is the velocity constant? IN which direction does gravity act?
Btw, the angle of the throw is not given?
 
g acts in y direction. velocity is constand is x direction. angle of throw, as mentioned, is perpendicular to the ground, and sincs cos90 = 1 it can be neglected.

i need help solving it.
 
siddharthmishra19 said:
g acts in y direction. velocity is constand is x direction. angle of throw, as mentioned, is perpendicular to the ground, and sincs cos90 = 1 it can be neglected.

i need help solving it.
Just list what you know
[itex]a_x = 0, a_y = -9.80 m/s^2, x_i=y_i=0, x_f=60 m, y_f =-80 m, v_{yi}=0[/itex] and what you are looking for is [itex]v_x[/itex].

Just write the equations along x and along y that you will need. Notice that you will have to find the time as well. So the idea is to find the time using the y equation and then use that in the equation along x to find the velocity.
 
thanks, all done
 
In the same problem, what is the time taken by the body to attain a velocity twice its initial velocity?

What is the displacement of the body at that time?
 

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