- #1
starstruck_
- 185
- 8
Hi! So someone came up to me with this question during physics and its been bothering me because I didn't know what to say to them and I didn't know if my understanding is correct or not. The question was something like:
" A 72 kg car is traveling at v=63km an hour when it gets into a collision, coming to a stop in d= 14 m.
Calculate the magnitude of the net force applied on the car. When I did my whole equation rearranging stuff using 0= v1^2+2(-a)d
I got a= v1^2/(2a) and hence, force = ma= m(v1^2/(2d)).
When I did it I was like okay great got everything I need, I'm good to go so I didn't really think about the signs of my answers, so I really didn't knoe what to say to the person who asked me why the signs were positive when, when you're stopping and set the direction of your displacement as positive, your force and acceleration come put negative even though they're opposing your motion.
I tried to give an answer in that we've already accounted for the fact that acceleration is negative in our initial expression, but if we were to put it back into v2^2=v1^2+2ad we would put in the negative of the answer and that we changed that plus sign to a minus sign so we accounted for the negative direction of the acceleration and just need the positive magnitude? I don't know.
It made sense to me mathematically so :/
Can someone help out? This is really bothering me for some reason
" A 72 kg car is traveling at v=63km an hour when it gets into a collision, coming to a stop in d= 14 m.
Calculate the magnitude of the net force applied on the car. When I did my whole equation rearranging stuff using 0= v1^2+2(-a)d
I got a= v1^2/(2a) and hence, force = ma= m(v1^2/(2d)).
When I did it I was like okay great got everything I need, I'm good to go so I didn't really think about the signs of my answers, so I really didn't knoe what to say to the person who asked me why the signs were positive when, when you're stopping and set the direction of your displacement as positive, your force and acceleration come put negative even though they're opposing your motion.
I tried to give an answer in that we've already accounted for the fact that acceleration is negative in our initial expression, but if we were to put it back into v2^2=v1^2+2ad we would put in the negative of the answer and that we changed that plus sign to a minus sign so we accounted for the negative direction of the acceleration and just need the positive magnitude? I don't know.
It made sense to me mathematically so :/
Can someone help out? This is really bothering me for some reason