Frisky90 said:Homework Statement
The brakes on a car are applied when traveling at 55km/h and it comes to rest uniformly in a distance of 50m. The mass of the car is 800 kg . Calculate the braking force and the time for the car to come to rest.
Homework Equations
F=ma
v=u+at
t=s/v=50*3.6/55=3.27s
0=55/3.6 +a*3.27
a=-4.67 deceleration. Then F=800*4.67=3738.2263N braking force
However, according to the txtbook the right answers are: 1.87kN, 6.55s ?
Apphysicist said:Watch your units...your kinematics equations deal with m/s and m/s/s. You have km/h.
Also, from an energy standpoint, I verified that 1.87kN is correct for the force.
Chronos said:You have used distance traveled inappropriately. The correct way to plug in distance is
a = (v^2 - u^2) / 2s
where v is final velocity, u is intial velocity, and s is distance traveled.
The equation of motion is a mathematical expression that describes the relationship between an object's position, velocity, and acceleration over time. It is commonly written as S = ut + (1/2)at^2, where S is the object's displacement, u is its initial velocity, a is its acceleration, and t is time.
Displacement is the straight-line distance between an object's initial and final positions, while distance is the total path length traveled by the object. For example, if an object moves 10 meters east and then 5 meters west, its displacement is 5 meters east, but its distance traveled is 15 meters.
Speed is a measure of how fast an object is moving, while velocity is a measure of both speed and direction. In other words, velocity takes into account the object's movement in a specific direction, while speed does not. For example, a car traveling at a constant speed of 60 mph north has a velocity of 60 mph north, while a car traveling at a constant speed of 60 mph in a circular path has a velocity of 60 mph but is constantly changing direction.
Acceleration is the rate of change of an object's velocity over time. In the equation of motion, acceleration is represented by the term at^2, which shows that the object's acceleration is directly proportional to the square of the time. This means that the longer an object accelerates, the greater its change in velocity will be.
The equation of motion can be used to predict an object's future position and velocity based on its starting conditions. This is particularly useful in physics and engineering, where it can be used to design and analyze the motion of objects such as cars, airplanes, and projectiles. It can also be used in everyday situations, such as calculating the time it will take to reach a destination based on your speed and distance traveled.