# AP Physics 1: 1.3 Changes and Conservation Laws

AP Physics 1: 1.3 Changes and Conservation Laws. How fast is the particle falling at the instant before it hits the ground?

AP Physics 1 | Changes and Conservation Laws |

Language | English Language |

Science Practice 2 | Using math appropriately |

### Transcript

down a ramp and she tours on only often adds

it is twenty meters tall if it's moving it twenty

five meters a second in ways fifteen kilograms is it

shoots off the edge How fast is it falling at

the instant before it hits the ground right near the

potential answers All right well just be interesting So how

do we combine the horizontal speed of an object with

its vertical speed from gravity to find out how fast

it's falling thinking about terminal velocity here Well actually we

don't combine them at all It doesn't matter how fast

an object moves for izon aly the acceleration of gravity

is a constant downward force They'll consider this if a

bullets fired from a gun on a perfectly horizontal plane

and at the same time a bullet drops from a

hand at the same height as the gun Both bullets

Will hit the ground at the exact same instant Pretty

cool huh Yeah So let's address this question by first

looking at the potential energy of the particle Potential energy

remember equals mass times gravity times height All right well

when we plug our numbers into that equation we see

that the potential energy of this particle at the moment

it leaves the ramp is three thousand jewels So speaking

gravitationally the total mechanical energy at the moment the particle

leaves the ramp is three thousand jewels After all mechanical

energy equals potential energy plus kinetic energy And at the

very instant the particle leaves the ramp it hasn't started

falling yet So the kinetic energy is zero So what

will the kinetic energy be right before the particle hits

the ground Well at that point there will be no

more potential energy So if the total mechanical energy of

this system is three thousand jewels and the potential energy

is zero then the kinetic energy will have to be

three thousand jewels We have to remember the formula for

kinetic energy which is kinetic energy equals one half mass

times velocity squared right here saying wake unplugging our numbers

and solve for velocity Well three thousand jewels equals one

half times fifteen kilograms Times velocity squared little algebra and

we'll see that the velocity is twenty meters a second

So the correct answer is option a When dealing with

falling objects potential energy is pretty much always involved Remember

how to calculate it and remember how it relates to

connecticut and mechanical energies but leave falling objects to theoretical

problems In the real world they tend to cause issues 00:02:38.733 --> [endTime] now