Calculating Acceleration of a Sphere Thrown Upward

[ch3570r]

I know I already have a topic for a previous question, but here's another simple one, but I think I am just missing some simple equations.

"What is the magnitude of acceleration after 1.5 seconds of a sphere thrown upward from a height of 13 meters at 20 m/s^2?"

Choices
a) 5.3 m/s^2
b) 9.8 m/s^2
c) 15 m/s^2
d) 32 m/s^2
e) 390 m/s^2

I realize these are quite obvious answer choices, and the answer is most likely D, but I don't know how to get it. I only have the "four kinematics" equations to work with, but I think there are other equations I can use for this. How does the height of 13m effect my answer, if it indeed does.

 

[courtrigrad]

Use the equation y = y_{0} + v_{y0}t + \frac{1}{2}a_{y}t^{2}

 

[ch3570r]

Use the equation y = y_{0} + v_{y0}t + \frac{1}{2}a_{y}t^{2}

ok, using that equation, doesn't it leave me with two unknowns? I have time, initial distance in y, and initial velocity in y. I don't have the total distance in y, or the acceleration, which I am trying to find. Is that right, or am I mistaken...I might need to find total distance first, and then the acceleration.

 

[d_leet]

I know I already have a topic for a previous question, but here's another simple one, but I think I am just missing some simple equations.

"What is the magnitude of acceleration after 1.5 seconds of a sphere thrown upward from a height of 13 meters at 20 m/s^2?"

Choices
a) 5.3 m/s^2
b) 9.8 m/s^2
c) 15 m/s^2
d) 32 m/s^2
e) 390 m/s^2

I realize these are quite obvious answer choices, and the answer is most likely D, but I don't know how to get it. I only have the "four kinematics" equations to work with, but I think there are other equations I can use for this. How does the height of 13m effect my answer, if it indeed does.

What causes the object to accelerate? What is the magnitude of this acceleration? This is more of a "did you memorize this constant?" kind of question than a problem about applying kinematics equations. Lastly why do you think it's D?

 

[ch3570r]

well, the acceleration down would be gravity (9.8 m/s^2)...wait, so the answer is B!? I was thinking that because the object is traveling at 20m/s^2, after 1.5 seconds, it would be slighty over 20m, and the closest answer is D. But I guess if its asking for the "magnitude" of the acceleration, it would be gravity.

 

[d_leet]

well, the acceleration down would be gravity (9.8 m/s^2)...wait, so the answer is B!? I was thinking that because the object is traveling at 20m/s^2, after 1.5 seconds, it would be slighty over 20m, and the closest answer is D. But I guess if its asking for the "magnitude" of the acceleration, it would be gravity.

Yes the answer is B. And no after 1.5 seconds the object is not traveling at 20m/s^2 that is an acceleration not a velocity! Acceleration is measure in units of meteres per second squared and near the surface of the Earth the value of acceleration due to gravity is nearly constant at 9.8m/s^2.