View Full Version : I need a physicist

26-03-2006, 10:36:33
Well, I need someone to test drive a problem I'm going to set my year 10 class tomorrow...

Using the formulas for kinetic energy (K.E. = x mass x velocity^2) and
gravitational potential energy (G.P.E = mass x gravity field strength x height)
complete the following calculations

Gravity field strength is 10 N

1: How much gravitational potential energy does a 500kg
rollercoaster car have at after climbing 25 metres?

2: The rollercoaster car rolls down the track and drops 20 meters.
How much potential energy does it have now?

3: If there was no friction or air resistance and all the lost
potential energy has all been converted into kinetic energy how
fast is the rollercoaster car moving?

4: In fact the roller coaster car was travelling at 10m/s.
How much kinetic energy does the car have?
How much energy has been lost as friction and air resistance?
What form is this energy likely to be in?

Obviously its rather better laid out and has proper ^2 symbols etc. They have done the K.E. formula already and will do the G.P.E. stuff in the in the first part of the lesson, this is the harder question for the 2-3 bright ones in a middle set.

26-03-2006, 17:09:20
come on guys, or have you all forgotten the easy stuff?

Immortal Wombat
26-03-2006, 17:11:13
I haven't done physics since year 10. Easy stuff is all I ever had to remember.

1/ Depends what height it started at. ;) The amount it has gained is 500*10*25 = 125000 J

2/ The amount it has lost since Q1 is 500*10*20, so the amount it has (relatively) is 500*10*5 = 25000 J

3/ KE = 100000 = .5*500*v^2
=> v = 20m/s

4/ .5*500*100 = 25000 J
75000 J
mostly heat, some sound

26-03-2006, 17:26:10
I didn't see what the question was?


26-03-2006, 17:42:47
Cheers - IW. Thats the same answers I got, and if you havnt done it since yr 10 then I've got the level about right. I changed the first question to how much energy it gained which is better.

26-03-2006, 21:17:01
2.not much
3.like an effin bullet
4 a) a fair amount
b) plenty
c) speed

:lol: :clueless:

27-03-2006, 02:04:44
Gravity field strength is 10 N

Errr...grav field strength is measured in acceleration (m/s^2) not force (N = kgm/s^2). Assuming you meant 10m/s^2, IW's answers are correct

27-03-2006, 08:13:35
yeah, I was wondering about that