The discussion revolves around calculating the total force exerted by a car with a mass of 1500 kg that is decelerating at 15 m/s². Participants are exploring the relevant forces acting on the car, including gravitational force and frictional force, and how these forces interact with the road.
There is an ongoing exploration of the forces acting on the car, with some participants providing guidance on the importance of identifying the direction of forces. Multiple interpretations of the problem are being discussed, particularly regarding the implications of the deceleration value and its physical feasibility.
Participants note potential constraints such as the assumption that the car is not generating force due to a possible accident scenario, and there is a mention of typical limits for road cars regarding deceleration forces.
Redbelly98 said:Try drawing a free body diagram of the car. What are the forces that are present, and in what direction are they?
Also, in what direction (horizontal or vertical) does the car decelerate? Which force or forces are acting in that direction?
Redbelly98 said:Yes: gravity downwards, normal force from ground upwards, and friction force horizontally. And two of those forces are exerted by the ground, so the car exerts equal-but-opposite forces on the ground.
kthejohnster said:a car of mass 1500kg and decelerating 15ms-2. what is the total force of car on road from all tires?
The two forces act in different directions, x or y, so we can't simply add them. But yes, they turn out to be equivalent to mg and ma -- I guess this is what you were saying in your first post. But technically you need to say in what direction those forces are acting. So for the 15,000 N force you calculated from mg, in what direction does it act? Likewise for the 22,500 N force you calculated from ma.kthejohnster said:so would that be mg+ma because opposite of gravity would be mg and the force opposite friction seems to be ma or is there a separate y force and x force
While you bring up a valid point, since this is intro physics it's probably best to keep things simple; neglect air resistance, and use the numbers given. It's likely that the question author was not thinking through about the implications of a 1.5g acceleration due to friction -- or the 15 m/s2 was a simple typo.cmb said:Difficult to tell. I expect this is not the answer the question is looking for, but it means you are in the process of having an accident so your tyres might not be generating any force at all!
I do not believe your tyres can generate 1.5g (I think the limit for road cars is around 1.1g with latest tech), unless you are in a race car with aerodynamic downforce, but then the car wouldn't weight more than 605kg. (due to Formula 1 construction rules 605kg or Formula 3 540kg.)