Maximum Speed Question

In summary, the conversation discusses a problem involving a car accelerating at -10 m/s^2 and the driver needing to apply the brakes after seeing a barrier 40 m ahead. Various equations are used to determine the maximum speed possible for the car in this scenario. Ultimately, the solution is found to be 21.76 m/s or approximately 78 km/h.
  • #1
NMiller5a
2
0
I've been trying for about an hour to figure this one out and decided that I should probably ask some people who know what their doing for some input.

"A driver of a car suddenly sees the lights of a barrier 40 m ahead; it takes the drive 0.75 s to apply the brakes; the car accelerates at a speed of -10 m/s^2. What is the maximum speed possible?"

I decided to break the problems into two parts; first, the total distance covered during the time prior to initiating of braking and the time after. For the former part I was left with (Vo)(0.75). The latter part I ended with Vo(Vo/10)+0.5(-10)(Vo)^2. I put those together and 40=(Vo)(0.75)+Vo(Vo/10)+0.5(-10)(Vo)^2. Did I create an incorrect equation?
 
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  • #2
Welcome to PF!

I think the second part of the equation is incorrect.

You are trying to use s = ut + 0.5 a t^2, right?

You shouldn't as that is 1 equation with two unknowns - you don't know what s is, and you don't know what t is.

Instead, use v^2 = u^2 + 2*a*s, and seen where you get from there.

PS: You know SUVAT terminology, right?
s = displacement
u = initial velocity
v = final velocity
a = acceleration
t = time
 
  • #3
Thank you for your prompt reply and assistance!

I changed my equation into v=u^2+2(a)(s) and it worked very well. 0=u^2+2(-10)(40-0.75u)] worked perfectly and I got an answer of 21.76 m/s, or about 78 km/h.

When the time comes that I'm only 40 meters away from an inescapable barrier I'll know if I'm doomed or not...
 

What is "maximum speed"?

"Maximum speed" refers to the highest possible velocity that an object can achieve in a given situation. It is often used to describe the fastest speed that a vehicle or animal can reach.

How is maximum speed measured?

Maximum speed is typically measured in units of distance per time, such as miles per hour or meters per second. It can be calculated using various methods, such as radar guns or timing devices.

What factors affect maximum speed?

The maximum speed that an object can achieve is influenced by various factors, including the object's mass, shape, and the amount of resistance it encounters. Other factors such as air density, surface conditions, and propulsion force can also impact maximum speed.

Can maximum speed be exceeded?

In theory, there is no limit to how fast an object can travel. However, in practice, the laws of physics and practical limitations such as the strength of materials and human capabilities make it difficult to exceed certain speeds.

Why is maximum speed important?

Maximum speed is important in various fields, including transportation, sports, and engineering. It helps determine the performance and capabilities of different objects and can also be used to set safety standards and regulations.

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