How Do Birds Control Their Falling Speed and Cars Stop Quickly?

[Big Rudy]

Actually, I guess I have two questions...

OK, if a 2 Kg bird wants to drop at a rate of 1.2 m/s^2, what is the magnatude and direction of the force that the bird must exert?

(Answer is 17.2 N, but I don't understand what work to do to get it)

As for the second: If a car with a mass of 800 Kg traveling at 20 m/s slams on the breaks and comes to a complete stop after 1.5 seconds, what is the force the car feels?

(Answer is 10,667 N,but I don't understand what work to do to get it)

Any help is greatly appreciated. And if helping others doesn't make you happy, at least mastering these problems will make you feel smart.

 

[russ_watters]

The first problem is f=ma (or a=f/m) and the second is that plus a=s/t

 

[Doc Al]

Originally posted by russ_watters
... and the second is that plus a=s/t

I'm sure russ meant a=v/t.

 

[Big Rudy]

I figured the problems out the morning they were due. But thanks for the help anyway.