|
An 800-kg car moving with a speed of 28 m/s (at A) puts on the brakes and slows down to a speed of 14 m/s (at B). Use g = 10 N/kg to perform an energy analysis and fill in all the blanks.
(Note: Your numbers were randomly selected and likely different from the numbers listed here.)
|
|
Work - Mechanical Energy Relationships:
If non-conservative forces do net work upon an object, then the total mechanical energy of that object is changed. The sum of the kinetic and potential energies will change as work is done upon the object. The amount of work done on the object by non-conservative forces is equal to the amount of change in mechanical energy.
|
|
Like all questions in this mission, the work done by non-conservative forces must be related to the changes in energy of the object (see Know the Law section). In the case of the car slowing down, the kinetic energy equation (see Formula Frenzy section) can be used to determine the initial and final kinetic energy of the car. Since the car is on the ground, the height and potential energy can be regarded as zero. The change in mechanical energy is caused by and equal to the work done upon the object. By calculating the change, the work can be determined. As mentioned in the question statement, enter a negative answer if the work is negative.
|
|
The amount of kinetic energy (KE) possessed by an object depends upon its mass (m) and its velocity (v). The formula is
KE = 0.5 • m • v2
The amount of potential energy (PE) possessed by an object depends upon its mass (m) and its height (h). The formula is
PE = m • g • h
where g is the gravitational field strength (9.8 N/kg on Earth).
|