splitlight
New member
- Joined
- Feb 10, 2012
- Messages
- 1
Got this question in a past mechanics paper:
A car travelling at 10m/s starts to accelerate 12 metres before leaving a built-up area. The acceleration of the car t seconds later is given by (7.5-2t)m/s/s. How long will it be before the speed of the car reaches 20m/s, and how far outside the built up area will the car then be?
I know finding the derivative of a displacement gives you a velocity, deriving velocity gives you acceleration. And integrate to go the other way.
I integrated the acceleration to give me 7.5t -t2 +C. Would I be right in thinking C=10 because when t=0 the velocity of the car is 10m/s?
so then I did 7.5t -t2 +10 = 20
and end up with a nasty quadratic that is not solvable.... What have I done wrong?
Any help will be much appreciated. thanks in advance.
A car travelling at 10m/s starts to accelerate 12 metres before leaving a built-up area. The acceleration of the car t seconds later is given by (7.5-2t)m/s/s. How long will it be before the speed of the car reaches 20m/s, and how far outside the built up area will the car then be?
I know finding the derivative of a displacement gives you a velocity, deriving velocity gives you acceleration. And integrate to go the other way.
I integrated the acceleration to give me 7.5t -t2 +C. Would I be right in thinking C=10 because when t=0 the velocity of the car is 10m/s?
so then I did 7.5t -t2 +10 = 20
and end up with a nasty quadratic that is not solvable.... What have I done wrong?
Any help will be much appreciated. thanks in advance.