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CONFUSED!!!
At a race track, a car of mass 2000 kg crashes into a concrete wall at a speed of 77 m/s.
a. If the car comes to a stop when it hits the wall, what is the magnitude of the impulse applied to the car?
b. To make things safer, the race track installs barrels of sand along the wall. If the car crashes into the barrels, the time it takes to stop will be increased by a factor of 3, as compared with hitting a concrete wall. How does this affect the force applied to the car during a crash?

Respuesta :

barnuts

A. Impulse is simply the product of Force and time. Therefore,

I = F * t                                 ---> 1

where I is impulse, F is force, t is time

 

However another formula for solving impulse is:

I = m vf – m vi                    ---> 2

where m is mass, vf is final velocity and vi is initial velocity

 

Therefore using equation 2 to solve for impulse I:

I = 2000kg (0) – 2000kg (77 m/s)
I = -154,000 kg m/s

 

B. By conservation of momentum, we also know that Impulse is conserved. That means that increasing the time by a factor of 3 would still result in an impuse of -154,000 kg m/s. So,

I = F’ * (3 t) = -154,000 kg m/s

Since t is multiplied by 3, therefore this only means that Force is decreased by a factor of 3 to keep the impulse constant, therefore:

(F/3) (3t) = -154,000 kg m/s

 

 

Summary of Answers:

A. I = -154,000 kg m/s

B. Force is decreased by factor of 3

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