Question

A 0.145 kg baseball is launched at an angle of 30 degrees and strikes the ground at 18 m/s. How fast would it be moving when it reaches the ground if its launch angle was 45 degrees.Ignore air resistance.

Answer 1

@roadjester

Answer 2

210 m/s. 18 m/s. 340 m/s. 16 m/s.

Answer 3

I'm thinking 210 m/s or 16 m/s

Answer 4

is there any other information?

Answer 5

initial velocity maybe?

Answer 6

nothing :/

Answer 7

what chapter are you on in physics?

Answer 8

energy

Answer 9

so what do u suggest the answer could be? Cause I have those two options but not sure

Answer 10

@roadjester

Answer 11

i'm here genius; i'm thinking

Answer 12

lol no sarcasm I actually am smart and good with math and literature just that physics or science overall is the only subject I don't understand

Answer 13

you do realize that physics is just an extension of calculus right?

Answer 14

yeah but I haven't taken calc yet they're making me take physics before

Answer 15

\[\large E_i=E_f\]
\[\large K_f+U_f=K_i+U_i\]
\[\large {\frac 1 2 mv_f^2}+{mgh_f}={\frac 1 2 mv_i^2}+{mgh_i}\]

Answer 16

ok, so you're currently in the energy aspect of your class; in this particular problem, it's assumed that energy is conserved. As such, initial energy is equal to the final energy. Energy is composed of both kinetic energy, in which there is velocity, and potential energy.

Answer 17

In the meantime could you check if my answer for this is correct : which of these follows from newton's laws about the energy of a moving object

The kinetic energy of an object remains the same if friction is absent.

The total mechanical energy of an object is always constant.

The mechanical energy remains the same if there are only conservative forces acting.

The total of all forms of energy is always constant

My answer is D

Answer 18

am I correct?

Answer 19

to me the wording is somewhat vague; i hate conceptual questions...

Answer 20

so am I wrong?

Answer 21

i never said that; let me think sheesh

Answer 22

@ybarrap
I actually think the answer to @QueenBee232 's second question about Newton is C. What do you think?

Answer 23

@ybarrap ?

Answer 24

Trick question. The velocity when it hits the ground is the same same as the initial velocity, regardless of angle. They give you total velocity, that is x-velocity and y-velocity vectors combined and this will be the same at launch because we assume that the vertical distance is the same at the beginning and end of the trip.

Answer 25

ok so the answer for the first one would be then?

Answer 26

Initial velocity = final velocity

Answer 27

18 m/s?

Answer 28

yes - does this make sense?

Answer 29

yes :) I remember now about the beginning being equal to the end

Answer 30

cool and as for the second question?

Answer 31

I think it's D but @roadjester thinks its C

Answer 32

The sum of all energy is constant because of the conservation of energy. For example, kinetic initial + potential initial = kinetic final + potential final = constant.

Answer 33

ok...

Answer 34

so that would make D correct or A?? :/

Answer 35

@ybarrap

Answer 36

...

Answer 37

Not A because kinetic energy does not constitute ALL forms of energy, which remains constant.

Answer 38

ok so B

Answer 39

1 minute left then practice closes

Answer 40

B C or D

Answer 41

D

Answer 42

According to the law of conservation of mechanical energy, the mechanical energy of an isolated system remains constant in time, as long as the system is free of friction and other non-conservative forces.

Answer 43

So there are really two best answers, C and D

Answer 44

The law of conservation of energy states that the total energy of an isolated system cannot change—it is said to be conserved over time. So it remains constant, but it must be isolated. Because D does not state this, C is the best answer.

Here is why:

http://en.wikipedia.org/wiki/Mechanical_energy#Conservation_of_mechanical_energy
http://en.wikipedia.org/wiki/Conservation_of_energy

Answer 45

There is only one reasonable answer: it's not going to be the same as at 30 degrees, and it's not going to be 10 to 15 times as fast, either.