Posted by Misty on Thursday, January 19, 2012 at 11:33am.
You are on roller blades on top of a small hill. Your PE is 1,000.0 Joules. The last time you check your mass was 60.0 kg. What is the height of the hill?
if you start skating down this hill, your poetntial energy will be converted to kinetic. At the bottom of the hill, the kinetic energy will be equal ot your potential energy at the top. What will be your speed at the bottom of the hill? What is a Joule?
8th grade physical science - drwls, Thursday, January 19, 2012 at 12:06pm
1 Joule is a unit of energy or work. It equals 1 Newton*meter or 1 kg*m^2/s^2. They all mean the same thing.
When you use physics equations with length measured in meters, time in seconds and mass in kg, you will end up with work and energy with units of joules. It is important to know that.
If 1 kg is moving at 1 m/s, its kinetic energy (K.E.) is 0.5 joules, since
K.E. = (1/2) M V^2.
To answer your other questions,
the height of the hill is
H = 1000 J/(M*g) = 1.70 meters. That is a very small "hill" !
If the kinetic energy at the bottom is 1000 J, then
(1/2)M*V^2 = 1000
V^2 = 33.33
V = 5.77 m/s
The fastest sprinters can run at about 10 m/s
8th grade physical science - Steve, Thursday, January 19, 2012 at 12:07pm
A Joule is the energy used to apply i Newton for 1 meter. J = Nm
A Newton is the force needed to accelerate 1 km at the rate of 1m/s^2. That is, to increase its velocity by 1m/s every second.
PE = mgh
1000 = 60*9.8*h
h = 1.7m (small hill indeed!)
KE = 1/2 mv^2
1000 = 1/2 * 60 * v^2
v^2 = 33.333
v = 5.77m/s
8th grade physical science - PS - Steve, Thursday, January 19, 2012 at 12:08pm
Newton moves 1kg, not 1km!
8th grade physical science - Misty, Thursday, January 19, 2012 at 1:46pm
Thank you so much, now I can try to help my child with her 12 problems. I needed that refresher.
8th grade physical science - Misty, Thursday, January 19, 2012 at 4:04pm
Did I do these one correctly?
A baby carriage is sitting on top of a hill that is 21 m high. The carriage with the baby wieghs 12N. Calculate the energy?
PE= 252 Nm or do i multiply by 9.8m/s^2?
8th grade physical science - Steve, Thursday, January 19, 2012 at 11:41pm
no, the N includes the g. 12N = mg
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