Question

Bob throws a 0.50 kg baseball straight up. At a height of 30.0 m it is moving at 12m/s
a) what is the ball's kinetic energy?

b) What is the gravitational potential energy of the ball?

c) How much work was done by Bob to get the ball up into the air?

Answer 1

m=0.50 kg
h=30 m
v=12m/s

a. apply the kinetic energy formula \(\sf KE= \frac{1}{2}mv^2\)
b. apply the potential energy formula \(\sf PE= mgh \), where g is the acceleration due to gravity.
c. apply work energy theorem: \(\sf W=\Delta E\)

Answer 2

Thank you for mentioning the formulas. I already know how to use them, I did part a and b, but not c. Could you please explain me how to do it?

Answer 3

@Michele_Laino

Answer 4

I do not know how to do C.

Answer 5

I'm pondering...

Answer 6

Ok. My teacher gave me the answer. He did not show the work. Do you want the answer? Maybe it can help you to find how?

Answer 7

ok!

Answer 8

46) a) 36J
b) 150J
c) 180J

Answer 9

part a)
\[KE = \frac{1}{2}m{v^2} = \frac{1}{2} \times \frac{1}{2} \times 144 = 36Joules\]

Answer 10

Yes

Answer 11

part b)
\[PE = mgh = \frac{1}{2} \times 10 \times 30 = 150Joules\]
here g=10 m/sec^2

Answer 12

Yes

Answer 13

It is challengic! :D

Answer 14

yes! Lol!
for part c) we can write this equation:
\[\Large \frac{1}{2}mv_{INITIAL}^2 - \frac{1}{2}mv_{FINAL}^2 = mgh\]

Answer 15

No,

Answer 16

where v_FINAL= 12 m/sec

Answer 17

ok go on

Answer 18

and v_INITIAL is the starting speed of your ball

Answer 19

Starting speed is o m/s

Answer 20

I think

Answer 21

it is impossible, since v_INITIAL =0 then the ball can not go away

Answer 22

Then how the answer is 180J? You are tight it is impossible.

Answer 23

One more question? it is important for me to know.

Answer 24

easy for you

Answer 25

I think that it is an approximated value, since the work done by Bob has to be equal to the initial kinetic energy

Answer 26

namely:
\[W = \frac{1}{2}mv_{FINAL}^2 + mgh = 36 + 150\]

Answer 27

W is change in kinetic energy, but not mechanical energy. It is fine, we can move to another question.

Answer 28

May I ask you my another question?

Answer 29

W is the work done by Bob.
more explanation:
if the ball is thrown by a compressed spring, then we can say that the potential energy of the spring is equal to the kinetic energy of the ball, so the work done by the spring on the ball is equal to the initial kinetic energy of our ball

Answer 30

the same reasoning goes if we replace the spring with Bob

Answer 31

Ok. Makes sense.

Answer 32

Can I ask you one more question. It is important for me to know for my exam

Answer 33

ok!

Answer 34

I open a new question

Answer 35

ok!