Verification of a problem -> force needed for car stopping in 1.8cm

[simphys]

Homework Statement

picture

Relevant Equations

newton's 2nd law of motion F_net = ma
Kinematic equation: v_fx^2 = v_0x^2 + 2*a_x*(deltaX)

hello guys can someone verify my solution (in the picture) whether the solution is correct or I guess the steps followed would be enough. There is no solution in the book for this one but wanted to be sure.

Thanks in advance

 

[kuruman]

You used 37 m/s for the initial velocity of the car when it is given as 37 km/h. The method is correct.

 

[mjc123]

Why does your homework statement talk of a 850 kg car traveling at 45 km/h when the question you copy says a 840 kg car traveling at 37 km/h?
Note v₀ = 37 km/h, NOT 37 m/s!
First rule of any test is READ THE QUESTION ACCURATELY.

Edit; kuruman got there first!

 

[simphys]

You used 37 m/s for the initial velocity of the car when it is given as 37 km/h. The method is correct.

Why does your homework statement talk of a 850 kg car traveling at 45 km/h when the question you copy says a 840 kg car traveling at 37 km/h?
Note v₀ = 37 km/h, NOT 37 m/s!
First rule of any test is READ THE QUESTION ACCURATELY.

Edit; kuruman got there first!

Thanks guys, appreciate it! And well no.. I mistakenly copied the wrong question. I typed it in google but found a question on cheg from the same book (other edition) with just the numbers changed hence why, my apologies

 

[Lnewqban]

Then, you have three practical limitations to that strong braking effect:
1) Friction between tires and asphalt.
2) Excessive negative acceleration (g-force) for passengers.
3) Excessive heat in brake pads-discs.

 

[Mike S.]

Lnewqban: That's why you need to supply your own brick wall (or borrow a neighbor's). The car *can* stop on a dime, though.

 

[kuruman]

I don't see why advertise a car that can stop on a dime. Its air bags would have to be deployed every time it did so. If it doesn't have air bags for that reason, its driver can stop on a dime exactly once in a lifetime.

 

[simphys]

Then, you have three practical limitations to that strong braking effect:
1) Friction between tires and asphalt.
2) Excessive negative acceleration (g-force) for passengers.
3) Excessive heat in brake pads-discs.

Thanks for the indication that.

Lnewqban: That's why you need to supply your own brick wall (or borrow a neighbor's). The car *can* stop on a dime, though.

I presume that that was sarcastic

 

[Lnewqban]

Thanks for the indication that.

Velocity used in the calculation should be 10.28 m/s.

After you calculate the force necessary to stop in 1.8 cm, just for curiosity, you could see how much force the maximum available static friction (rubber-asphalt μ is around 0.8) would actually allow, as well as how big of g-force the passengers would experience.

 

[Orodruin]

its driver can stop on a dime exactly once in a lifetime.

While this may be true for the spirit of the idiom, if taken literally the driver can do it many many times. Stopping on a dime would technically just require you to be on top of it as you come to a rest.

 

[simphys]

Velocity used in the calculation should be 10.28 m/s.

After you calculate the force necessary to stop in 1.8 cm, just for curiosity, you could see how much force the maximum available static friction (rubber-asphalt μ is around 0.8) would actually allow, as well as how big of g-force the passengers would experience.

wow that's insane very curious how this these coefficients for the frictions are calculated (I guess looking at the molecular interaction between both surfaces explains that.. and lots of experimentation ofc)