# Momentum and Collision with a seat belt

• ankurx13
In summary, the conversation involves a request for help with two physics questions. The first question involves calculating the force exerted on a 12kg child during a collision, using the formula v=u+at and the mass and acceleration. The second question involves finding the speed and direction of two protons after an elastic collision.
ankurx13
Need some help, got a 50 question review packet of questions to finish and am having trouble with these 2. please and thank you:

1. A friend claims that as long as he has his seat belt on, he can hold on to a 12.0-kg child in a 60.0 mi/h head-on collision with a brick wall in which the car passenger compartment comes to a stop in 0.0500 s. Show that the violent force during the collision will tear the child from his arms.

2. A proton, moving with a velocity of vii, collides elastically with another proton that is initially at rest. If the two protons have equal speeds after the collision, find (a) the speed of each proton after the collision in terms of vi and (b) the direction of the velocity vectors after the collision.

i would really appreciate some help guys.

ok so for question 1
what you want to figure out is the force exerted by the 12kg as it decelerates from 60->0 in.05 seconds

there is a formula that says
v=u+at
which means your final velocity is equal to your inital velocity plus acceleration multiplied by time
so knowing that your final velocity is zero and time is .05 you can work out "a"

which is about 30 odd m/s [prob a bit less than that]

anyway point is you now have "a"
you also know the mass of the child which i'll call "m"

now you calculate the force required to produce this acceleration [or deceleration] for this mass.
F=ma

i'm guessing it would be like trying to lift a half ton. anyway your neck would probably break.
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## 1. What is momentum and how does it relate to seat belts in a collision?

Momentum is a measure of an object's mass and velocity. In a collision, the momentum of an object can change due to a change in its velocity. Seat belts are designed to help reduce the change in momentum of a person during a collision, thus reducing the force exerted on their body and potential injuries.

## 2. How does wearing a seat belt affect the momentum of a person in a car crash?

Wearing a seat belt can greatly reduce the change in momentum of a person in a car crash. The seat belt acts as a restraint, slowing down the person's forward motion and increasing the time it takes for them to come to a stop. This decrease in the person's change in momentum also decreases the force exerted on their body, reducing the risk of injury.

## 3. Can a seat belt prevent a person from getting injured in a car crash?

A seat belt cannot completely prevent a person from getting injured in a car crash, but it can greatly reduce the severity of their injuries. By reducing the force exerted on the person's body, seat belts can help prevent injuries such as whiplash, broken bones, and head trauma.

## 4. How does a seat belt affect the collision between a person and the car's airbag?

In a collision, the seat belt restrains the person's body and prevents them from moving forward too quickly. This allows the airbag to deploy and cushion the impact, rather than the person's body absorbing the full force of the collision. Without a seat belt, the person may hit the airbag with a much higher momentum, increasing the risk of injury.

## 5. Are there any other factors besides a seat belt that can affect momentum and collisions in a car crash?

Yes, there are several other factors that can affect momentum and collisions in a car crash. These include the mass and velocity of the vehicles involved, the angle and speed of impact, and the use of other safety features such as airbags and crumple zones. Additionally, the use of distractions, such as texting while driving, can greatly increase the risk of a collision and impact the momentum of the vehicles involved.

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