Does anyone want to help me with these problems on Kinetic and Potential Energy?

Question

1.An object has a mass of 5 kg. Calculate its potential energy 3m above the ground.
2.Calculate the kinetic energy of a 1000 kg car traveling at 60km per hour.
3.A mass of 20g is 30cm from the floor. How much potential energy it have?
4.How much kinetic energy does a 150 N (Newton) barrel have upon striking the ground from a height of 5m?
5.How much current flows through a lamp with a resistance of 90 ohms when it is connected to a 120 V (Volt) outlet?
6.What is the resistance of a lamp which allows 0.8 A () current when 110 V (Volt) is applied to it?
7.Find a speed of sound in air at 30 C (Celsius).

I need clear solutions. thanks! :)

I am having a hard time with 4,5,6,7. Can someone explain it to me?

Answer 1

Hello! I will do the best I can to help you......


First let me give you the two formulas needed to solve these problems:

KE = 1/2mv^2 OR m*v^2/2

PE = m * g * h (mass x gravity x height) HOWEVER.....

If the displacement occurs vertically, raising an object off of the ground let's say, we term this Gravitational Potential Energy. We can calculate the gravitational potential energy of an object with this formula:

GPE = mass x height

Also.......KE AND PE are both measured in Joules(J) the unit of energy.

1. GPE = m * h
= 5kg * 3m
= 15J

2. KE = m * v^2/2
= 1000kg * 60kmph^2/2
= 1000 * 3600/2
= 3600000/2
= 1,800,000J

3. (G)PE = m * h
= 20g * 30cm
= 600J

4. Please look back at the wording for this question. I believe that there is a time measurement missing in order to plug in the velocity. I made an assumption and went ahead with it here using meters/sec.

KE = 1/2mv^2
= 1/2(150N)(5m/s?)^2
= 1/2(150)(25)
= 1/2(3750)
= 1875J

***the next 3 problems are not PE and KE problems, but I will do them as well***

Resistance = R measured in ohms
Current = I measured in amperes
Voltage = V measured in volts

R = V / I ; V = I(R)

5. V = I(R)
120 = I(90)
120/90 = I
1.333amperes = I

6. R = V / I
R = 110 / 0.8
R = 137.5 ohms

7. Speed of Sound in Air
The speed of sound in dry air is given approximately by
v sound in air ~ 331.4 + 0.6Tc m/s

where Tc is the celsius temperature,

so that at temperature 30C

the speed of sound is approx. 349.4m/s

This sound speed does not apply to gases other than air.

It is important to note that the sound speed in air is determined by the air itself. It is not dependent upon the sound amplitude, frequency or wavelength.

I included the web links for several of the sites I consulted. I hope that they are helpful to you!
Good luck!

Answer 2

Sorry, can't give you exact answers - if I did, you wouldn't learn the material....I can however, give you several formulas to use with questions 5 and 6....in these formulas, E = Voltage, R = Resistance, I = Current, and P = Watts, so remembering those, if you have 2 of them, then you can figure out another 1 of the values....here's the formulas....E = I times R, I = E divided by R, R = E divided by I, P = I times E. Hope that helps and as far as anything else....good luck.

Answer 3

Potential energy in earth's gravity is mass*g*elevation.
Kinetic energy of a mass m moving at velocity v is .5*m*v^2
For part 4, 150N is the mass times g of the barrel. The kinetic energy when it hits the floor 5m down is equal to the potential energy lost in that 5m (see potential energy definition above).

Ohm's law: Voltage (volts) = current (amps) times resistance (ohms)

Speed of sound see http://en.wikipedia.org/wiki/Speed_of_sound

Answer 4

1. 147 Joules
Potential Energy Formula - E(p) = mgh
m = Kilograms
g = Force of Gravity
h = height in meters

2. 1.8 X 10^12 Joules, or 1,800,000,000,000 Joules
E(k) = (1/2)mv^2
m = Kilograms
v = velocity

3. 0.0588 Joules
4. 3675 Joules
5. 1.3 repeating decimal, amps of current flow.
I = V/R
I = Current in amps
V = Voltage in Volts
R = Resistence in Ohms

6. 137.5 ohms
7. I definitely don't know this one, haven't studied much with the speed of sound in air conditions... It's on my to-do list.

Answer 5

1. m = 5 h = 3 and g = 10
P.E. = mgh
= 5 x 3 x 10
= 150 J
2. m = 1000 v = 60
K.E.

Answer 6

Answer 1)
potential energy=
mass*gravity*height

5*9.8*3=potenergy=147

Answer 7

as much as i am tempted to give you solutions i won't because it probably won't help you any. i found that struggling with the problem and figuring it out is the best way to learn..please check out the website below...perhaps it will give you a clear understanding on the material..i think it would be nice if you're more specific with what part you are struggling. please try the problems yourself first..it would be easier to help you that way

http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/energy/u5l1c.html

Answer 8

NO NOT REALY