In need of homework help please, it has to do with force and velocity?

Question

A 1000-kg car is moving 30 m/s. A braking force of 6000 N is applied for 4.0 s. What is the velocity of the car when the brakes are released?

How do you do this

Answer 1

6 m/s

Answer 2

U better giv me 10 points coz jez answer and no working and not detected by ur psychic teacher means he's not fit 2 teach physics:

Impulse= force*time because Newton's 2nd Law says:

Rate of change of momentum= for(mv-mu)/t = F

where m is mass of object, v is final velocity and u is initial velovity, F is force exerted on object.

So cross multiply: Impulse= F*t= mv-mu
Taking direction of motion as that of u, F will have to be negative because a braking force opposes initial motion of car in u or fwd direction and slows down a car by acting in opposite backward direction. Therefore if u stipulate u as positive, so will v but F will be -ve and m will have no direction as its scalar. Comprendez?

(/ms stands for metres per second)
(/ms2 stands for per ms2 squared)

-6000kg/ms2*4s = 1000kg(v-30)m/s
-24000kg/ms = 1000kg(v-30)m/s

Do unto LHS what thee did to RHS which is basically divide both sides by 1000kg so you are left with eqn on speeds. Similarly add 30ms toeach side:
-24 ms = v-30
-24+30 = v ms
6 ms = v

Answer 3

You need to use the following formulae:
f=ma where f=force m=mass a=acceleration.
From this you can work out the deceleration under the braking force.

Now you can use v=u+at where u=initial velocity, v=final velocity, t=time.

Remember acceleration is negative if a body is slowing down.

Answer 4

MV=FT so
(1000 kg)(Vf-30 m/s)=(-6000N)(4s)
6 m/s=Vf