APPLYING NEWTON’S 2ND LAW TO
Body systems
•When two objects are connected by a
rope or chain, applying a force on one
Watch out for
of the objects will cause both objects to
Neatorama
accelerate
at the same rate and in the
factsdirection.
on Sir
same
Isaac
Newton!
•We solve
the question by assuming the
applied mass is acting on a ‘single’
object whose mass is equivalent to the
Total Mass!
1. Baby Newton Wasn’t Expected to Live…..
Two body questions can be vertical or
horizontal!
Ex 1) Two blocks of identical material are connected by a light rope
on a level surface. An applied force of 55 N [right] causes the blocks to
● Since the boxes are attached by a wire, they
accelerate. While in motion, the magnitude of the force of friction on the
accelerate
at the
same rate. We
block system must
is 44.1
N. Calculate
the acceleration
of thecan
blocks.
also treat them as one big mass instead of two
small masses.
● We will assume that the wires have no mass.
● Fg and FN cancel each other vertically, so we
can ignore them.
● To the right is positive, and to the left is
negative.
Ex 2) Refer to the diagram above. The force of friction on the 10-kg block
has a magnitude of 14.7 N.
(a) Calculate the tension in the rope connecting the two blocks.
(b) Calculate the tension in the rope between the hand and the 10-kg block.
2. Newton Almost Became a Farmer
Two body systems cont’d…
Ex3) Two buckets of nails are hung one above the other and are pulled up
to a roof by a rope. Each bucket has a mass of 5.0 kg. The tension
in the rope connecting the buckets is 60 N. Calculate the acceleration
of the buckets.
Ex 4) Two boxes are attached by a thin wire as shown in Drawing 3. A person pulls on
the wire attached to the yellow box. There is a force of friction of 213 N acting on the
boxes. Determine the force applied to the boxes if they accelerate to the right at 2.45
m/s2.
3. Newton and His Apple: The True Story
Applying Newton’s 2nd law to Single
Pulley Questions….. Atwoods Time!



“Atwood's Pulley” is a classic physics problem involving two unequal
masses hanging from a wire over a pulley.
When m1 = m2, the machine is in neutral equilibrium regardless of the
position of the weights
To be continued
Ex 5) If mass one is 12.00 kg and mass two is 7.50
kg, determine
the acceleration
of each mass.
on Next
Slide…
When m1 ≠ m2 both masses experience uniform acceleration but in the
direction of the larger mass.
● We will need to be careful, since the net force is
pulling the blue box down and the yellow box up, but is
made up of two forces due to gravity pulling down on
different sides.
● To simplify this, we will take our single mass and
pretend that one forcedue to gravity is pulling it to the
left, while the other force due to gravity is pulling it to
the right.
Example 5 Continued- Atwoods
pulley…
4. Newton was Secretive - He Rarely Published
Offfspring of the Newton’s Apple Tree in Woolsthorpe Manor
Whatever happened to the mama tree? The King’s School in
Grantham, Linconshire, England, where Newton went to school, claimed
to have purchased the tree and moved it to its garden.
Ex 6) A 6.0 kg flower pot and a 4.0 kg flower pot are tied
together and suspended from a pulley.
a. What is the net force in the system?
HINT! We must find the force on each pot
And then find the net force on the system!
b. what is the acceleration of the 6.0 kg pot?
HINT: Because the pots are tied together we must
use the total mass.
A:
6.0
kg
c. what is the acceleration of the 4.0 kg pot?
5. Newton was Deeply Religious …
B:
4.0
kg
Ex. 7) Two objects, A and B, are connected by a light rope over a light,
frictionless pulley. A has a mass of 25 kg and B a mass of 35 kg. Determine
the motion of each object once the objects are released.
6. He was
an Alchemist!
Remember to use total mass when calculating Fnet!
7. Newton Battled Counterfeiters
Applying Newton’s Second law to a TwoPulley System
Ex 8)
8. Newton the Politician Uttered Just One Sentence