# Homework Help: Would someone explain this in general terms?

1. Nov 12, 2007

### roguel33ter

Just registered on these forums because I need some physics help!

Teacher doesn't explain things adequetly(sp?)

So how do you solve these problems in general terms?

"A 4:24 kg mass attached to a light string
rotates on a horizontal, frictionless table. The
radius of the circle is 0:548 m, and the string
can support a mass of 16:2 kg before breaking.
The acceleration of gravity is 9:8 m=s2 :
What maximum speed can the mass have
before the string breaks? Answer in units of
m=s."

"If the gravitational force between the elec-
tron (of mass 9:11 £ 10¡31 kg) and the proton
(of mass 1:67 £ 10¡27 kg) in a hydrogen atom
is 5 £ 10¡48 N, how far apart are the two par-
ticles? The universal gravitational constant is
6:673 £ 10¡11 N ¢ m2=kg2. Answer in units of
m."

2. Nov 12, 2007

### Kurdt

Staff Emeritus
Can you show what you've attempted so far?

For the first question you know what tension the string will support so you can work out the centripetal force that would be equal to that tension and thus derive how fast the mass can go.

For the second question all you need is Newton's universal law of gravitation and rearrange some terms.

http://hyperphysics.phy-astr.gsu.edu/hbase/grav.html#grav

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