# Variable acceleration - help please!

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#1
Hi, I've done this question and was wondering if what I've done is correct? It feels like I've made it up...

Here is the question:
https://hosting.photobucket.com/imag...t_21.12.51.png

My working:
a) If P does not come to rest, v cannot equal 0
b^2 - 4ac = -31
-31 is less than 0, so the equation has no real roots and v is never 0

b) dv/dt = 4t - 3
0 = 4t - 3
t = 3/4
Sub t into original equation for v, v = 3.875 ms^-1
Last edited by NaBrO; 1 month ago
0
1 month ago
#2
(Original post by NaBrO)
Hi, I've done this question and was wondering if what I've done is correct? It feels like I've made it up...

Here is the question:
https://hosting.photobucket.com/imag...t_21.12.51.png

My working:
a) If P does not come to rest, v cannot equal 0
b^2 - 4ac = -31
-31 is less than 0, so the equation has no real roots and v is never 0

b) dv/dt = 4t - 3
0 = 4t - 3
t = 3/4
Sub t into original equation for v, v = 3.875 ms^-1
👍 It all looks good to me, and is exactly what I'd have done.
1
1 month ago
#3
(Original post by NaBrO)
Hi, I've done this question and was wondering if what I've done is correct? It feels like I've made it up...

Here is the question:
https://hosting.photobucket.com/imag...t_21.12.51.png

My working:
a) If P does not come to rest, v cannot equal 0
b^2 - 4ac = -31
-31 is less than 0, so the equation has no real roots and v is never 0

b) dv/dt = 4t - 3
0 = 4t - 3
t = 3/4
Sub t into original equation for v, v = 3.875 ms^-1
Looks fine.

As an alternative method, you could just complete the square. This would give you all the information at once, though perhaps slightly longer working.
0
#4
(Original post by ghostwalker)
Looks fine.

As an alternative method, you could just complete the square. This would give you all the information at once, though perhaps slightly longer working.
Thank you!
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