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Review - Explain this using one of Newton's Laws

 

 

 

 

 

A lead brick has a lot of mass
and therefore a lot of inertia.

The greater the mass, the greater the tendency for an object to remain at rest, the smaller the acceleration that is produced by a given force.

 

 

 

Momentum Word Problems

 

J = Ft = mΔv = Δp

 

 

 

Ex 1)  A 5.0 kg mass has its velocity change from 8.0 m/s east to 2.0 m/s east. 

Find the objects change in momentum.

 

Ex 1)  A 5.0 kg mass has its velocity change from 8.0 m/s east to 2.0 m/s east.  Find the objects change in momentum.

 

m = 5.0 kg
Vi = 8.0 m/s East
Vf = 2.0 m/s East
Δp = ?

 

 

J = Ft = mΔv =Δp

 

 

Δp = mΔV

 

 

= (5.0 kg)(2.0 m/s - 8.0 m/s)

 

= -30. kgm/s East

 

or +30. kg m/s West

 

 

 

 

Ex 2) A 5.0 kg mass moving with a velocity of 8.0 m/s east has an impulse applied to it which causes its velocity to change to 20. m/s East.   Find Impulse:


Ex 2) A 5.0 kg mass moving with a vector of 8.0 m/s east has an impulse applied to it which causes its velocity to change to 20. m/s East.

 

Find Impulse:

m = 5.0 kg
Vi = 8.0 m/s East
Vf = 20. m/s East
J = ?

 

J = Ft = mΔv =Δp


J = mΔv = (5.0 kg)(12. m/s East)

 

= 60. kg m/s east


= 60. Ns East

 

 

 

Find the force if the impulse was applied for 3.0 sec.

 

F = ?

t = 3 seconds

m = 5.0 kg

Vi = 8.0 m/s East

Vf = 20. m/s East

J = 60. kg m/s east

 

 

J = Ft = mΔv =Δp

 

J = Ft = 60. Ns East

 

F(3.0 sec) = 60. Ns East

 

 

F = 20. N East

 

 

 

 

Golf Ball hitting steel super slo mo

School Blocks YouTube? Click below.

GolfBallhittingsteelsuperslomo.mp4

 

 

 

 

Ex 3) How long would it take for a net upward force of 100. N, to increase the speed of a 50. kg object from 100. m/s to 150. m/s.

 

Ex 3) How long would it take for a net upward force of 100. N, to increase the speed of a 50. kg object from 100. m/s to 150. m/s.

 

 

F = 100. N

m = 50. kg

Vi = 100. m/s

Vf = 150. m/s

t = ?

 

J = Ft = mΔv =Δp

 

 

 

FΔt  = mΔv

 

 

 

(100. N)t  =  50. kg(50. m/s)

 

 

t  =  25. secs

 

 

Ex 4)  A 1.0 kg ball traveling @ 4.0 m/s strikes a wall and bounces straight back @ 2.0 m/s.

Find Δp

 

 

 

ballRebound

 Racquetball Slow-Mo - HiViz

 

 

Ex 4)  A 1.0 kg ball traveling @ 4.0  m/s strikes a wall and bounces straight back @ 2.0 m/s

Find Δp 

 

m = 1.0 kg

Vi = 4.0 m/s

Vf = ?

Vf = -2.0 m/s

(opposite direction)

Δp = ?

 

 

J = Ft = mΔv =Δp

 

 

(a) Δp = mΔv

 

 

= (1.0 kg)(-2.0 m/s - 4.0 m/s)

 

 

= - 6.0 kgm/s

 

 

(b) What is impulse applied to the ball?   


 

J =  Δp = -6.0 kgm/s

 

 

 

 

(c) What is impulse applied to the wall?

 

J = +6.0 kgm/s

 

 

3rd Law, Action Reaction

 

Computer animation of a Newtons' cradle

DemonDeLuxe (Dominique Toussaint)

 

 

 

 


 

 

 

 

 

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Photo credit: Photo by Dan Little © HRL Laboratories, 

 

 

 

AP Physics

p. 188) 17

 

Dp = mDv

 

Momentum only changes in the x direction

toward wall +

Vi = Vsinq

Vf = -Vsinq

Dp = mDv

Dp = m(-2Vsinq)

 

= 2.1 kgm/s left

 

Review

A teacher pushed ice cubes of different masses with different amounts of force. Which diagram shows the cube that will show the biggest velocity change when pushed with the force represented by the arrow?
A) A
B) B
C) C
D) D
E)
To find the velocity change, you need the force's contact time.

 

 

 

[Law Of Conservation

 Of Momentum]

 

 

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