Physics collisions question?

Question

Suppose a child drives a bumper car head on into the side rail, which exerts a force of 2400 N on the car for 0.500 s. (Assume the initial velocity is in the positive direction.)
(a)
What impulse (in kg · m/s) is imparted by this force? (Indicate the direction with the sign of your answer.)
  
Incorrect: Your answer is incorrect.
 kg · m/s
(b)
Find the final velocity (in m/s) of the bumper car if its initial velocity was 2.90 m/s and the car plus driver have a mass of 200 kg. You may neglect friction between the car and floor. (Indicate the direction with the sign of your answer.)
  m/s

electron1 · Accepted Answer

As the bumper car hits the side rail, its velocity will decrease. This means the force is negative.

There are two equations for impulse.

Eq#1, Impulse = Force * time
Eq#2, Impulse = Mass * Change of velocity
This is the change of momentum.

Impulse = -2400 * 0.5 = -1200 kg * m/s

(b) 
Find the final velocity (in m/s) of the bumper car if its initial velocity was 2.90 m/s and the car plus driver have a mass of 200 kg. You may neglect friction between the car and floor. (Indicate the direction with the sign of your answer.) 
m/s

The first step is to determine the acceleration.

-2400 = 200 * a 
a = -12 m/s^2

Let’s use the following equation to determine the final velocity.

vf = vi + a * t
vf = 2.90 + -12 * 0.5 = -3.1 m/s

The negative sign means the bumper car is moving away from the side rail after the collision. I hope this is helpful for you.

Physics collisions question?

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