A car of mass 1330 kg is traveling at 28.0 m/s. The driver applies the brakes to bring the car to rest over a distance of 79.0 m. Calculate the retarding force acting on the car.
same as before just posting again so you wont have to scroll. heres my work
KE=1/2*m*v^2
KE=521360
KE=Ff*d
521360*Ff*79.0
521360/79.0
6599.5=Ff
I have to convert that to N, so
6599.5*9.80
= 64675 N what did I do wrong this time?
6599.5=Ff
That IS in Newtons
The 9.8 is acceleration of gravity, used to calculate the weight in Newtons of something on earth surface given the mass in kilograms. It is not needed here. There is no weight involved here, only mass and change of momentum.
thank you. great explaination
To calculate the retarding force acting on the car, you need to use the equation:
Force (F) = mass (m) * acceleration (a)
In this case, the acceleration is the deceleration caused by the brakes. To find the acceleration, you can use the kinematic equation:
v^2 = u^2 + 2as
where v is the final velocity (0 m/s since the car comes to rest), u is the initial velocity (28.0 m/s), a is the acceleration (which is what we're trying to find), and s is the distance traveled (79.0 m).
Rearranging the equation, we get:
a = (v^2 - u^2) / (2s)
a = (0 - 28.0^2) / (2 * 79.0)
a = -784/158
a = -4.969 m/s^2
Since the deceleration is in the opposite direction of motion, we take the negative sign.
Now, you can substitute the mass (1330 kg) and the acceleration (-4.969 m/s^2) into the force equation:
F = m * a
F = 1330 * (-4.969)
F = -6598.37 N
So, the retarding force acting on the car is approximately -6598.37 N. Note that the negative sign indicates that the force is acting in the opposite direction of motion.