November 14, 2011
Check for understanding
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Two protons are separated by a distance of 1 X 10 m.
Find the gravitational attraction between the two particles.
November 14, 2011
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Exams returned
Goals Card updated
Universal Gravitation
Intro to Work & Energy
***Mid Term next Tuesday!
Review booklet handed out in class
Booklet to be turned in on exam day
November 14, 2011
Universal Gravitation
d2 or r2 is fine
Mass of Earth in Ref Table
Radius of Earth in Ref Table
CHECK THEM NOW!
November 14, 2011
HW P. 90 QQ 4.2
P. 91 Q 4.3 & Ex 4.3
P. 109-110 MC #5 & 14
P. 122 Q 5.1 & EX 5.1
Quick Quiz 4.2
Which has a greater value, a newton of gold won on the Earth or
a newton of gold won on the Moon? B -on the Moon
P. 91 Q4.3 & Ex 4.3
Q 4.3: Mars is 1.5X as far from the sun as the Earth. What if Fsun
on a 70kg man standing on Mars? Fsun = 0.2N for man on Mars
Ex 4.3: Find the force exerted by the Moon on a 70kg man
standing on Earth. Fmoon = 0.002N for man on Earth
P. 109 & 110 MC #5 B & #14 B
P.122 Q5.1 & Ex 5.1
Q 5.1: How does the work change if the load is doubled?
Assuming dounble load produces doubled frictional force, BUT Ff is VERY
small, doubling load probably will not change effort force or distance, thus
keeping work approx the same as before.
Ex 5.1: Suppose the sled is pushed instead on level terrain with a
force of 50N.
o
a.) Force exerted at an angle of 0 to the horizontal, distance =?
to do 400J of work 8m
o
b.) Force exerted at 45 angle to the horizontal, how much work
for the same amount of distance? 283m using Fx as the force
November 14, 2011
P. 91 Q4.3 & Ex 4.3
Q 4.3: Mars is 1.5X as far from the sun as the Earth. What if Fsun
on a 70kg man standing on Mars?
Ex 4.3: Find the force exerted by the Moon on a 70kg man
standing on Earth.
November 14, 2011
November 14, 2011
An object has a mass of 10.2kg.
Find the weight of the object (force
due to gravity) on the surface of the
Earth, at one Earth radius above the
surface, two Earth radii, and 3 Earth
radii.
November 14, 2011
Calculate the force of gravity between you and the person sitting next to you in class,
assuming you both have masses of 60 kg and are sitting 1.2 m apart.
Two tennis balls have a mass of 0.25 kg each and they are placed so that there is a distance
of 42 cm between their centers. What is the gravitational force between the two tennis balls?
Use the universal gravitation formula to find the weight of a 10 kg object on the surface of the
earth.
2
At what altitude above the earth’s surface would the acceleration due to gravity be 4.9 m/s ?
A 14.2 kg object weighs 6.55 N at a certain point above the earth’s surface.
(a) What is the acceleration due to gravity at that point?
(b) How far is the object from the earth’s surface?
(c) What is the weight of the block on the earth’s surface?
November 14, 2011
November 14, 2011
A certain hypothetical2 planet has a radius of 500 km and a surface gravitational
acceleration of 3 m/s . (a) What is the mass of the planet? (b) What is the
gravitational acceleration 100 km above the surface of the planet?
How far from the surface of the earth must a satellite be in order to have a weight
of only 1/3 of its weight at the earth’s surface?
What is the weight of a 14 kg object when it is 300,000 m above the surface of
Mars?
November 14, 2011
1. It is the gravitational force that holds a planet in its orbit
about the Sun. If it were zero, the planet would continue in
a straight path rather than following an ellipse. Gravity is
the string on the yo-yo when it is spun in a circle...
2. Fg = 81.26N
3. Fg= 81.7N
4. Fnew = 9 Fold
5. Fnew = 9/4 Fold
6. Fnew = 1/9 Fold
7. Fnew = 4/9 Fold
8. Fnew = 1/8 Fold
9. Fg = 1641 N
a = 2.27 m/s2
and
10. Fg = 2 X 1020 N
11. Fg = 17354 N
skip 11c, 12 a & b
and
and
each pulls each
other with 2 X 1020N
a = 8.68 m/s2
November 14, 2011