Physics
posted by Jason
A car traveling 56 km/h is 24 m from a barrier when the driver slams on the brakes. The car hits the barrier 2s later
a) what is the car's constant deceleration before the impact?
b)How fast is the car traveling at impact?
I don't get the impact parts...
I think you have to use one of these formulas:
v=v0+at
xx0=v0t+1/2at^2
v^2v0^2=2a(xx0)
xx0=(v0+v)/2 *t
xx0=vt1/2 at^2
But I'm not sure if these are correct...
The question unanswered here is does the car hit the barrier? The velocity at impact is not known, therefor the acceleration cannot be determined (as if the brakes did not stop it). Now if one assumes the car stopped just at the barrier, then the final velocity is zero, so you know acceleration...
Vf^2=Vo^2 + 2*accelertion*distance and you can solve for acceleration.
The question b) is really the question, and it is cannot be determined. We assumed Vf was zero in part a. Something is flawed about the construction of this question.
Look at the formula xx0=(v0+v)/2 *t
Let x0=0 and x=24m and and t=2sec so
2*24m/2sec=v0+v or 24m/s=56m/s + v so v=32m/s I'm really not sure if this makes sense here. If so, then
(vv_0)/t=average deceleration so (3256)/2 = 88/2 =44m/s^2
Be sure to check that I use the formula correctly. See if there's an example in your book like this.
If we use this formula xx0=v0t+1/2at^2 then
24m=56m/s *2sec + (1/2)a(2sec)^2 so
2(24m112m)/4sec^2=44m/sec^2=a which agrees with the first result
If we use v=at+v0 with a=44m/sec^2 and t=2sec, v0=56m/s then
v=88m/s+56m/s=32m/s
It seems to agree also, but I'm not sure about the negative velocity.
Hopefully this helps...
Respond to this Question
Similar Questions

physics
A car traveling 56 km/h is 24 m from a barrier when the driver slams on the brakes. The car hits the barrier 2s later a) what is the car's constant deceleration before the impact? 
physics
a car is traveling at 40.0 m/s. the drivers sees an emergeny ahead and 0.50 s later slams on the brakes. the acceleration of the car is 4.0 m/s^2. a. what distance will the car travel before it stops? 
Physics
A car traveling 56 km/h is 21.0 m from a barrier when the driver slams on the brakes. The car hits the barrier 2.17 s later. a)What was the car's constant deceleration before impact? 
calc
a) A car is traveling at 50 mi/h when the brakes are fully applied, producing a constant deceleration of 40 ft/s^2. What is the distance covered before the car comes to a stop? 
Physics
A driver of a car going 90.0km/h suddenly sees the lights of a barrier 40.0 metres ahead. It takes the driver 0.75 seconds before she applies the brakes, and the average acceleration during braking is 10.0 m/s squared. Does the car … 
Physics
A car traveling 56 km/h is 22.0 m from a barrier when the driver slams on the brakes. The car hits the barrier 2.15 s later. (a) Assuming constant acceleration, what was the magnitude of the car's acceleration before impact? 
Physics
A car traveling 56 km/h is 22.0 m from a barrier when the driver slams on the brakes. The car hits the barrier 2.15 s later. (a) Assuming constant acceleration, what was the magnitude of the car's acceleration before impact? 
Physics
A 920kg car is 65m from a concrete barrier, travelling at 125km/h, when the driver notices and slams on the breaks. The frictional force acting on the car is 8500 N. Is ther driver able to stop the car before hitting the barrier. 
Physics
A driver of a car going 90 km/h suddenly sees the lights of a barrier 40.0 m ahead. It takes the driver 0.75 s to apply the brakes, and the average acceleration during braking is 10 m/s2. (a) Compute for the total displacement of … 
Physics
A car traveling 51.1 km/h is 29.6 m from a barrier when the driver slams on the brakes. The car hits the barrier 3.08 s later. (a) What is the car's constant deceleration magnitude before impact?