Stone Throw, Found answer but don't understand how ?

  • Thread starter Thread starter Monocerotis
  • Start date Start date
Click For Summary
SUMMARY

The discussion centers on the physics problem of determining the velocity of a stone thrown from a bridge with an initial vertical velocity of 4.0 m/s after 2.2 seconds, considering both upward and downward directions. The participant successfully calculated the downward velocity as 2.6 x 101 m/s using the formula Vf = Vi + Aav(Δt). However, confusion arises regarding the use of the same equation for both scenarios, particularly the sign change for initial velocity (Vi) when the direction is reversed. Understanding the underlying principles of acceleration due to gravity and vector direction is essential for grasping this concept.

PREREQUISITES
  • Basic understanding of kinematics and motion equations
  • Familiarity with the concept of acceleration due to gravity (approximately 9.81 m/s2)
  • Knowledge of vector quantities and their representation
  • Ability to manipulate algebraic equations
NEXT STEPS
  • Study the principles of kinematic equations in physics
  • Learn about vector direction and how it affects motion calculations
  • Explore the concept of acceleration due to gravity in different scenarios
  • Practice solving similar problems involving projectile motion
USEFUL FOR

Students studying physics, educators teaching kinematics, and anyone seeking to understand the principles of motion and acceleration in vertical throws.

Monocerotis
Gold Member
Messages
54
Reaction score
0

Homework Statement


A stone is thrown from a bridge with an initial vertical velocity of magnitude 4.0m/s/ Determine the stone's velocity after 2.2s if the direction of the initial velocity is (a) upward, and (b) downward. Neglect air resistance.

Homework Equations


Aav=Vf - Vi / Δt

Vi + Aav(Δt) = Vf

The Attempt at a Solution



b) 2.6 x 101m/s
Easy to find as you enter in the given information into the formula.

(a) on the other hand I have difficulty understanding. I attempted the problem, with this formula
(-Vi) + Aav(Δt) = Vf. The answer I got corresponds to the answer in text, but I don't really understand how that works. I'd like to know for similar problems in the future.
 
Physics news on Phys.org
You use the same equation to solve both problems, but if v_i is positive in b, it must be negative in problem a.
 
willem2 said:
You use the same equation to solve both problems, but if v_i is positive in b, it must be negative in problem a.

Yes that's apparently obvious, I want to understand why however. The "theory" behind it.
 

Similar threads

A stone is dropped from an ascending balloon...
  • · Replies 10 ·
Replies
10
Views
2K
Why do I keep getting friction coefficient as a negative?
  • · Replies 17 ·
Replies
17
Views
4K
Kinematics: Motion in One Direction: Car Chase
  • · Replies 9 ·
Replies
9
Views
3K
How Fast Was the Second Stone Thrown to Match the First at the Cliff Base?
  • · Replies 2 ·
Replies
2
Views
2K
Need help with this question regarding kinematics.
  • · Replies 6 ·
Replies
6
Views
2K
Throwing two stones, find the velocity of the second stone
  • · Replies 11 ·
Replies
11
Views
2K
Solving for Displacement when Jamilla Throws a Stone
  • · Replies 3 ·
Replies
3
Views
4K
What Determines the Meeting Point of Two Falling Stones?
  • · Replies 5 ·
Replies
5
Views
2K
Free fall velocity and distance
  • · Replies 34 ·
2
Replies
34
Views
4K
The point at which 2 vehicles meet
  • · Replies 22 ·
Replies
22
Views
3K