Newton Laws Scenario's
Identify which of Newton's three laws best explains why a passenger lurches forward in a bus when it suddenly stops.
What is Newton's First Law (inertia): passenger continues moving forward when bus stops.
A 2.0 kg mass accelerates at 3.0 m/s2. Calculate the net force. Include the units to receive credit!
F=ma=2.0×3.0
What is 6.0 N
A 0.50 kg ball moving at 4.0 m/s has what momentum? Include the units to receive credit!
p=mv=0.50×4.0
What is 2.0 kg-m/s
The unit for momentum.
What branch of the military does Ms. Graham serve in?
What is the U.S. Army.
A skateboarder pushes off the ground and accelerates forward. Which law describes the skateboarder's acceleration due to the push?
What is Newton's Second Law: push causes acceleration proportional to force and inversely to mass.
A 1500 kg car accelerates from rest to 3.0 m/s2. What force must the engine provide (neglect friction)? Include the units to receive credit!
F=ma=1500×3.0
What is 4500 N
A car has momentum of 10,000 kg-m/s. What would be the car’s new momentum if
a. its velocity were tripled
b. its mass were doubled (by adding more passengers and a greater load)
Include the units!
a. Velocity tripled
Momentum triples:
What is 30,000 kg-m/s
b. Mass doubled
Momentum doubles:
What is 20,000 kg-m/s
What are the units for each of the following:
Velocity - ?
Acceleration - ?
Force - ?
Mass - ?
What is:
Velocity - m/s
Acceleration - m/s2
Force - N
Mass - kg
Two factors that determine an object’s momentum.
What is Mass and Velocity
A book rests on a table and does not move. Which of Newton's laws explains this?
What is Newton's First Law. An object at rest stays at rest unless acted upon by an unbalanced force.
A person exerts a 50 N horizontal force on a 10 kg box on a frictionless surface. What is the box's acceleration? Include the units to receive credit!
a=F/m=50/10
What is 5.0 m/s2
Upon hitting a bat, a baseball has a change in momentum of 18.5 kg-m/s. What is the average force applied to the baseball if the time of impact is 0.00650 seconds? Include the units to receive credit!
Use the impulse-momentum relationship:
F=Δp/Δt
Substitute the values:
F=18.5/0.00650
What is 2846 N
Another term for change in velocity.
What is acceleration.
In which example are the forces balanced?
Example 1: Hitting a Baseball with a Bat
Example 2: Car Moving at Constant Speed
What is Example 2.
Explanation:
These forces cancel out → balanced, so the car keeps moving at the same speed. Unbalanced forces causes objects to accelerate (speed up or slow down).
A rocket accelerates upward as exhaust gases are expelled downward. Which law explains this? Describe both action and reaction forces in the rocket example.
What is Newton's Third Law: rocket expels gas downward (action); gas pushes rocket upward (reaction).
A 0.2 kg tennis ball is hit, giving it an acceleration of 120 m/s^2. What net force acted on the ball? Include the units to receive credit!
F=ma=0.2×120
What is 24 N
A 8-kg bowling ball rolling at 6 m/s strikes a stationary 5-kg bowling ball. If the 8-kg ball is moving forward at 3 m/s after the collision, what is the change in momentum of the 8-kg ball? Include the units to receive credit!
Initial momentum:
pi=8×6=48 kg-m/s
Final momentum:
pf=8×3=24 kg-m/s
Change in momentum:
Δp=pf−pi=24−48=−24 kg-m/s
What is -24 kg*m/s (the ball lost momentum).
__________ is the term used to describe the process of changing an object’s momentum.
What is Impulse.
Omari has a mass of 80 kg. He pushes on a 40 kg rock with a force of 150 N. What force does the rock exert on Omari? Which Newton Law is involved here?
What is 150 N and Newton's 3rd Law.
A hockey puck slides across ice and gradually slows to a stop even though no horizontal push continues. Use Newton's laws to explain why it stops and identify which law primarily describes the puck's deceleration.
Hint: 2 answers: 1. What force slows objects down? 2. The puck is decelerating.
What is Friction (external force) causes deceleration.
What is Newton's Second Law describes the acceleration (deceleration) due to net force.
A net horizontal force of 25 N produces an acceleration of 2.5 m/s2 on an object. What is the object's mass? Include the units receive credit!
m=F/a=25/2.5
What is 10 kg
A 0.15 kg baseball is pitched at 40 m/s and caught (brought to rest) in 0.02 s. Find the average force applied by the catcher's glove. Include the units!
Hint: Δp=m(vf-vi) then use that answer to solve...
*From your last reading* Newton’s 2nd Law connects force and momentum. The law can be written not just as F = ma but also as a statement about changing momentum: Force = change in momentum / time.
Δp=0.15(0−40)=−6.0 kg-m/s
Favg=−6.0/0.02=−300 N
What is −300 N (direction opposite motion)
In each force pair, there is an _____________ and ______________ force.
Hint: Newton's 3rd Law
An object accelerates 18.0 m/s2 when a force of 9.0 N is applied to it. What is the mass of the object? Which of Newton's Law is involved in this problem?
Include the units in your answer!
m= F/a= 9.0/18.0
What is 0.5kg and Newton's Second Law.