Question

NEED HELP IN PHYSICS!
- mechanical energy. please

Answer 1

A 200 kg car is traveling at 5 meters per second.
what is its total mechanical energy relative to the ground?

Answer 2

Mechanical energy is kinetic energy (KE) and potential energy (PE). Since the car is on the ground \(PE = 0\).

Therefore, \(ME = KE\) and \(KE = (1/2) \cdot m \cdot v^2\)

Answer 3

alright thanks & what about this one.

A constant force of 500 N is applied to 50m to the same car in the above question by its engine.

What is the new mechanical energy of the car, after the force was applied for 50 m?

Answer 4

Let's remember that\[W = \Delta U\]where \(\Delta U\) is the change in mechanical energy and can be both kinetic or potential. Let's also recall that\[W = F \cdot x\]Therefore, \[F \cdot x = KE_f - KE_i\]since the height of the car presumably doesn't change. \(KE_f\) is the kinetic energy of the car after the force has been applied and \(KE_i\) is the kinetic energy before.

Answer 5

What is its new kinetic energy? what is its new speed? what is the increase in its speed? and how much power was applied by the engine of the car if we took 5s to cover the above distance?

Answer 6

so then the new mechanical energy would be 25000 J ?

Answer 7

New kinetic energy if \(KE_f\) from above equation.

The new speed comes from the new kinetic energy. I'll assume you know you definition of kinetic energy.

The increase in it's speed is the difference between the old and new speeds.

Power is defined as work over time. Therefore, \[P = {W \over t} = {F \cdot x \over t}\]

Answer 8

That is the amount of the energy increases. Remember the car has energy before we increase, so this initial energy needs to be added to the increase. This can be seen in the equation I gave.

Answer 9

so for the new mechanical energy of the car, after the force was applied is the same? doesnt change?

Answer 10

No. New mechanical energy is\[KE_{new} = {1 \over 2} 200 \cdot (5)^2 + 500 \cdot 50\] This is the initial kinetic energy PLUS the added kinetic energy.

Answer 11

and so the new kinetic energy would be the answer to the new mechanical energy.?

Answer 12

Yes. They are the same in this case because the potential energy does not change.

Answer 13

and for the new speed what equation would i use?

Answer 14

\[KE = {1 \over 2} m \cdot v^2\]

Answer 15

so it would be 27500 = .5 *2000*v^2 ?

Answer 16

Yes. Then solve for v.

Answer 17

and for the increase of speed i just do whatever i got minus the beginning speed?

Answer 18

Indeed.

Answer 19

for the power applied which f *x do i use? the new one?