Calculating the velocity and acceleration given vector velocity at 1 second

[mdavies23]

Actually, this is a 2d situation, so what are dv_x /dt and dv_y /dt in this case? Can you figure out the numbers from what is given?

dvx/dt would be 0

 

[kuruman]

dvx/dt would be 0

Yes, it would be. What about dv_y /dt? You know it's constant and equal to g_Mars. How can you find a value for it? What do you need to know?

 

[mdavies23]

Yes, it would be. What about dv_y /dt? You know it's constant and equal to g_Mars. How can you find a value for it? What do you need to know?

The velocity at time t=2

 

[kuruman]

The velocity at time t=2

You need to know more than that. Remember what we said, "For every second that goes by, you add g_Mars m/s in the downward direction to whatever velocity is already there." Acceleration has to do with change in velocity. You cannot determine a change from just one number. Change is what you end up with minus what you start with. You need two numbers to find the change in v_y. One number is v_y at t = 2s. What could the other number be?

 

[mdavies23]

You need to know more than that. Remember what we said, "For every second that goes by, you add g_Mars m/s in the downward direction to whatever velocity is already there." Acceleration has to do with change in velocity. You cannot determine a change from just one number. Change is what you end up with minus what you start with. You need two numbers to find the change in v_y. One number is v_y at t = 2s. What could the other number be?

V_y at time t=1

 

[kuruman]

Yes. So what is the acceleration on Mars?

 

[mdavies23]

Yes. So what is the acceleration on Mars?

So would it just be 3.72 m/s^2?

 

[kuruman]

That would be the magnitude. Congratulations! You have answered part (b). Now onto part (a). Can you write the velocity in vector form at t = 2 s and t = 3 s?

 

[mdavies23]

That would be the magnitude. Congratulations! You have answered part (b). Now onto part (a). Can you write the velocity in vector form at t = 2 s and t = 3 s?

V_x would stay the same and then I would add 3.72m/s to V_y. so 2.00m/s i + 7.44 m/s j

 

[kuruman]

At what time is this velocity? Remember that at t = 2 s the ball is at maximum height traveling horizontally.

 

[mdavies23]

At what time is this velocity? Remember that at t = 2 s the ball is at maximum height traveling horizontally.

I thought it would be a time t=2s

 

[kuruman]

I thought it would be a time t=2s

It can't be at time t = 2s. Please read your post #12 and reconsider.

 

[mdavies23]

It can't be at time t = 2s. Please read your post #12 and reconsider.

Oh so V_y would be zero so the vector would look like 2.00 m/s i + 0 m/s j

 

[kuruman]

Right. That's at t = 2 s. What is the velocity at t = 3 s?

 

[mdavies23]

Right. That's at t = 2 s. What is the velocity at t = 3 s?

2.00 m/s i - 3.72 m/s j

 

[kuruman]

Very good! You are done with part (a). Time to move on to part (c). What do you need to know to find the initial speed and launch angle?

 

[mdavies23]

Very good! You are done with part (a). Time to move on to part (c). What do you need to know to find the initial speed and launch angle?

I need to know the velocity vector at t=0 then i could find the magnitude and direction o f it

 

[kuruman]

Right. Go for it. Remember that in 2 s v_y drops from its initial value to zero.

 

[mdavies23]

Right. Go for it. Remember that in 2 s v_y drops from its initial value to zero.

7.70 m/s at an angle of 75 degrees

 

[kuruman]

That looks right. What about part (d)?

 

[mdavies23]

That looks right. What about part (d)?

2*4 = 8m

 

[kuruman]

That's it. You're done with this one.

 

[mdavies23]

That's it. You're done with this one.

Thanks for everything