Solving Free-Fall Kinematics: Find Acceleration from Initial Speed

AI Thread Summary
The discussion focuses on determining the acceleration of a ball thrown downward with an initial speed of 20 m/s. It clarifies that acceleration is a vector quantity, emphasizing that while horizontal acceleration is zero, vertical acceleration is influenced by gravity. The key point is that the acceleration of any object in free fall is constant and equal to the acceleration due to gravity, approximately 9.81 m/s². The conversation highlights the distinction between horizontal and vertical motion in kinematics. Understanding these principles is essential for solving free-fall problems accurately.
sarah_615
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Homework Statement


A ball is thrown downward with an initial speed if 20 m/s on earth.
What is the acceleration of the ball?


Homework Equations


vf=a (change in time)t + vi


The Attempt at a Solution


well you have to find the velocity of then find acceleration. and acceleration is m/s^2
on my notes it says that the horizontal acceleration is 0 m/s/s since its being thrown downward, (in a horizontal direction) that's what is getting me confused.
 
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Acceleration is a vector quantity - i.e. it has a direction. So as the ball is being thrown downwards and the force (do you know what it is) is also acting downwards there isn't going to be a horizontal acceleration but there will be a vertical one :)

Does this help?
 
Last edited:


sarah_615 said:
What is the acceleration of the ball?
Hint: No calculation needed here. The acceleration of any object in freefall is the same. (What's the acceleration due to gravity?)
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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