Momentum Problems - Dynamics | Show Me The Physics

Warm-Up

In order for a tennis serve to have the maximum speed, the server needs a big force and a long _______________

Show Me The Physics
YouTube Channel

Momentum Word Problems

Problem 1

A 5.0 kg mass has its velocity change from 8.0 m/s east to 2.0 m/s east. Find the object's change in momentum.

↓

m = 5.0 kg
V_i = 8.0 m/s East
V_f = 2.0 m/s East
Δp = ?

J = Ft = mΔv = Δp

Δp = mΔV

= (5.0 kg)(2.0 m/s − 8.0 m/s)

= −30. kg·m/s East

= +30. kg·m/s West

Problem 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:

↓

m = 5.0 kg
V_i = 8.0 m/s East
V_f = 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
V_i = 8.0 m/s East
V_f = 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.
GolfBallhittingsuperslomo

Problem 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
V_i = 100. m/s
V_f = 150. m/s
t = ?

J = Ft = mΔv = Δp

FΔt = mΔv

(100. N)t = 50. kg(50. m/s)

t = 25. secs

Racquetball Slow-Mo - HiViz

Problem 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
V_i = 4.0 m/s
V_f = −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 kg·m/s

(b) What is impulse applied to the ball?

↓

J = Δp = −6.0 kg·m/s

(c) What is impulse applied to the wall?

↓

J = +6.0 kg·m/s

3rd Law, Action Reaction

Computer animation of a Newton's cradle
DemonDeLuxe (Dominique Toussaint)

World's Lightest Material
200 times lighter than styrofoam

HRL Laboratories - See the video

Using an innovative fabrication process developed at HRL, researchers created a "micro-lattice" structure of interconnected hollow tubes with a wall thickness of 100 nanometers, 1,000 times thinner than a human hair.

Download high resolution image. High resolution video is available upon request by emailing media@hrl.com.
Photo credit: Photo by Dan Little — HRL Laboratories,

AP Physics

p. 188, #17

Δp = mΔv

Momentum only changes in the x direction
toward wall +

V_i = Vsinθ
V_f = −Vsinθ
Δp = mΔv

↓

Δp = m(−2Vsinθ)

= 2.1 kg·m/s left