At an accident scene on a level road, investigators measure a car’s skid mark to be 88 m long. the accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. use this data to determine the speed of the car when the driver slammed on (and locked) the brakes. use the work-energy principle to solve this problem. (while you are doing the problem think about why the car’s mass does not matter.)

27 m/s

Explanation:

Given

car's skid length is 88 m long

coefficient of kinetic friction is 0.42

let the mass of car be m and v be the velocity with which it was running initially.

Friction force

work done by friction force =change in the kinetic energy of car

work done by Friction

Change in the Kinetic Energy

Mass of car does not matter because in the final expression m gets cancelled.

when a device is used in a circuit in which the voltage is 81 v, the current flowing through the device is 3 a. what is the resistance of the device?

a. 27 ω

b. 40.5 a

c. 243 ω

d. 243 a

the correct answer is a. 27

answer: 2×10^-2kg

explanation: density= mass per volume

vol=mass/density

converting to s.i units we have;

3÷1000kg = 0.003

1.5÷100m = 0.15

0.003/0.15 = 0.02kg