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# Deceleration formula

Mon 6 Jul, 2015 06:37 am
Need to calculate something for work. An object moving at 7 m/s decelerates to zero over a time of 1.71s. How far does it travel? Thanks.
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Type: Question • Score: 2 • Views: 1,079 • Replies: 4
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maxdancona

1
Mon 6 Jul, 2015 06:43 am
@Wilso,
Deceleration is a type of acceleration (with a negative value). So, you just use the acceleration formula).

Find the acceleration with
A = (Vfinal - Vinitial) / T
(Vfinal is 0 so the result will be negative).

Then plug the value for A into the normal formula

D = Vinitial * T + 1/2 * A * T ^ 2

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engineer

2
Mon 6 Jul, 2015 10:22 am
@Wilso,
Or you could say the average speed is three and a half meters per second and multiply the average speed times the time.
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tsg92

1
Wed 15 Jul, 2015 05:19 pm
@Wilso,
Assuming the deceleration is constant. Then
a(t)=A (A<0)
v(t)=7+At
v(1.71)=7+1.71A
A=-1.71/7
s(t)=7t-1.71/14 t^2
s(1.71)=7(1.71) - (1.71)^3/14=11.613 m (3dp)

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Wilso

1
Wed 15 Jul, 2015 06:20 pm
Thanks guys. I haven't had the chance to check the maths against the what I'm seeing at the machine yet. It'll be next week now.
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