How Do You Calculate Impulse and Force in a Rear-End Collision?

[DANIELLYMA]

A 75 kg man is sitting in his car at rest at the stoplight. He is rear-ended by another car and is accelerated to 3.0 m/s in 0.2s. What is the impulse on the man and his car?

I found the impuse on the man which was:

I = m(change v)

= 75(3.0 -0)
= 225 Ns

I found the Net force on the man:

Fnet = 225/change in time
=225/0.2s
=1125N

I also found acceleration which is 15 m/s^2

I'm stumped because I can't find a way to find the impulse of the man and the car without needing the mass of the car. Any help would be highly appreciated.

Thank you

 

[fliinghier]

are those the exact words of the problem?

perhaps the answer is in terms of m?

 

[ogb p]

for bringing this problem to my attention. I understand your confusion and will try my best to help you solve this problem.

Firstly, let's define impulse as the change in momentum of an object. In this case, the man and his car experience a change in velocity from 0 m/s to 3.0 m/s. Therefore, the impulse on the man and his car would be the same since they are both experiencing the same change in velocity.

Now, let's consider the equation for impulse, which is I = mΔv. As you correctly calculated, the impulse on the man is 225 Ns. However, since the man and his car are experiencing the same change in velocity, we can use this same value for the car's impulse as well. Therefore, the impulse on the car is also 225 Ns.

To find the net force on the man and the car, we can use the equation Fnet = Δp/Δt, where Δp is the change in momentum and Δt is the change in time. Since the man and the car have the same change in momentum, we can use the same value for Δp, which is 225 Ns. As for the change in time, we can use the given value of 0.2 seconds. This gives us a net force of 1125 N, as you correctly calculated.

In conclusion, the impulse on the man and his car is 225 Ns and the net force experienced by both of them is 1125 N. I hope this helps clarify the problem for you. If you have any further questions, please do not hesitate to ask. Keep up the good work in your studies!