physics- work and energy problem? (this is a tough one)?

Question

A car traveling along a level road at speed 'v' slams on the brakes and skids to a stop. If the force of friction on the car is half the car's weight, how far does the car slide? (Hint: Use the work-energy theorem and solve for 'd')

Answer 1

The work-energy theorem says that the change in kinetic energy (K) of the car is equal to the work done on it. The change in K is:
Knew-Kold = 0 - (1/2)mv^2 = -(1/2)mv^2

The braking force is half the weight of the car:
f = (1/2)mg

This force is directed opposite the motion, so the work done is negative:
W = -fd = -(1/2)mgd

Equating change in K to W and solve. The mass cancels out, but g remains in the answer.

Answer 2

A. the residing house makes use of a million kW = one thousand W = one thousand Joules each 2d. In n seconds it makes use of n * one thousand Joules. B. verify how plenty potential 250,000 residences makes use of in an afternoon. area A factors the potential utilized by utilising one residing house. How do you bypass from that to 250,000 residences? verify how plenty potential you get from a sq. meter, given which you get basically 15% of the 20 MJ (20 million Joules). the quantity of potential mandatory divided by utilising the quantity of potential you get from one sq. meter factors the form of sq. meters mandatory.