# tbr physics chapter 4 passage Vi question 38

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#### javksmith93

##### Full Member
7+ Year Member
For a given collision speed, heavier cars are safer in collisions than lighter cars. This statement is:
A. true, because acceleration is smaller.
B. false, because acceleration is smaller.
C. true, because impulse is larger
D. false, because impulse is larger.

I thought it would be D. Due to J=change in m*v. So a larger mass should equal a larger change. If a 100 pound car traveling at 5 miles before collision and say 1 mile after the collision the difference is 400 Newton seconds. Now compare this to a 50 pound car and we get 50*5-50*1 for a total of 200 Newton* seconds for the impulse.

Tbr says it is

Choice A is the best answer. "Safer in collisions" refers to a reduced risk of injury and damage to the occupants in a vehicle during a collision. Damage to the occupants occurs as a result of impact, so the goal of safety engineers is to reduce the average force of the impact that occupants experience when vehicles collide. Ifyou recall that impulse creates achange in momentum, then we can apply Amv = F average * impact Assuming all other factors to be equal except mass, for a given collision speed, a larger car mass means a smaller acceleration (longer braking time), and this will be less jarring to the occupants of the car, because the applied force of impact is spread out over a longer period of time. While a heavier car has a greater impulse, it is its lower magnitude of acceleration during collision that increases occupant safety. Occupant safety is enhanced by minimizing the impact force that passengers experience (which is achieved by building in crumple zones around the passenger compartment) and by maximizing the time over which the collision occurs (which is achieved by using airbags and collapsible surfaces). Safety in a collision actually has very little to do with car mass, relative to the other factors such as time and vehicle deformation. The

How do I know that the acceleration is smaller for the bigger car and where does that play in? Thanl you for your help kind stranger.

Impulse is the same, whether it's a mac truck or a fly hitting the windshield. They both experience the same impulse. It is only the smaller mass that experiences a larger acceleration.

Knowing that impulse is the same, you can eliminate C and D. Now, think about what vehicle would be safer to be in. The one that experiences a larger acceleration or a smaller acceleration. When a mac truck hits a fly, the fly experiences a greater acceleration (it stops) while the mac truck keeps going (therefore experiencing a much smaller acceleration itself). It's safer to be in the mac truck. It's safer to experience less acceleration.

1 user
Impulse is the same, whether it's a mac truck or a fly hitting the windshield. They both experience the same impulse. It is only the smaller mass that experiences a larger acceleration.

Knowing that impulse is the same, you can eliminate C and D. Now, think about what vehicle would be safer to be in. The one that experiences a larger acceleration or a smaller acceleration. When a mac truck hits a fly, the fly experiences a greater acceleration (it stops) while the mac truck keeps going (therefore experiencing a much smaller acceleration itself). It's safer to be in the mac truck. It's safer to experience less acceleration.
Ahh I was interrupting the question as a crash test ie both cars running into a bigger wall so your example helps.

Would the impulse be different if like I interrupted it where they where both running into a wall?

what do you mean by interrupt?

what do you mean by interrupt?
Ahh sorry typing on a swipe keyboard.

I meant to say interpret not interrupt.