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F=ma
Third Law
Weight
Friction
Concept questions
100
I kicked your behind, causing you to accelerate on the ice at 3.0 m/s^2. If your mass is 60 kg, how much force did I kick you with?
F=ma F=60*3 F=180 N
100
Someone slaps you in the face with 400 N. How much force does the person feel back onto his hand?
What is 400 N
100
The units that is used to denote weight.
Newtons
100
I am a Force of friction bigger in magnitude than Kinetic Friction
What is static friction
100
If I kick a basketball such that it hurt my foot, would it have hurt more, less or the same if I would have kicked a bowling ball instead with the same force?
the force is the same, therefore by the third law, the force exerted on your foot will be no different either. It would hurt the same.
200
I push you with a force of 2000 N. If you accelerated 11 m/s^2, what is your mass?
What is 180 kg?
200
Two people are pulling on a rope in opposite direction. One is pulling with 300 N and the other with -300N. What is the tension on the rope?
What is 300 N?
200
My *blank* never changes, no matter the gravity
What is matter?
200
Name 3 advantages and 3 disadvantages of a world without friction
disadvantages: cannot walk, no terminal velocity (freezing rain would hurt), cars would have no brakes, roads would be slippery. advantages: requires less energy to push something, calculations are made easy, planes couldn't fly
200
How can I experience zero-g on earth.
accelerate downwards at 9.81 m/s^2
300
What is the acceleration of a softball if it has a mass of 0.5 kg and hits the catcher's glove with a force of 25 N?
a = F/m a = 25/0.5 a = 50 m/s^2
300
Two cars hitting each other at 50 km/h is the same as one car hitting a brick wall at ? km/h
What is 50 km/h
300
The gravity of a planet when my mass is 60 kg, and I weigh 96 N.
What is 1.6 m/s^2
300
The friction force of an object is 800 N and it's coefficient of friction is 0.20, what is the normal force on this object?
Ff = uFn Fn = Ff/u Fn = 800/0.20 what is Fn = 4000 N
300
name 3 types of surface tensions (out of 6) with examples for each.
What is solid-solid, liquid-solid, gas-solid
400
A pitcher throws a 0.15 kg ball at 100 km/h. The time it took for the ball to go from rest to being released was 0.5 seconds. How much force did the pitcher exert on the ball?
Vi = 0 Vf = 100 km/h = 27.8 m/s t = 0.5 s a = (Vf-Vi)/t = 100/0.5 = 200 m/s^2 F = ma = 0.15*200 = 30 N
400
Name all of the third law pairs and use caveman talk to describe them: A bird on a leash attached to a tree
bird on leash, leash on bird leash on tree, tree on leash earth on bird, bird on earth
400
An astronaut is in a space ship, and decides to lift a refrigerator in the air since he know it has no apparent weight. However, it took more force than he initially thought. What did forget about?
Inertia
400
A book is being pushed against the wall at 200 N so that it doesn't slip. The static coefficient of the two surfaces is 0.45. What is the friction force that keeps the book from slipping?
Fn = Fapp Ff = uFapp Ff = 0.45*200 = 90 N
400
In zero-g, do you feel the blood rushing in your head if you're upside down? Why?
no, everything is being pulled down at the same rate.
500
Hussein Bolt's mass is 94 kg. He finished the 100 meter race in 9.58 seconds. Assuming his acceleration was constant (it isn't), how much average force must he have applied to the ground?
t = 9.58s d = 100m Vi = 0 d = 1/2at^2 a = 2*d/t^2 a = 2.179 m/s^2 ----> F=ma=94*2.179=205 N
500
Why was the horse able to pull the wagon if the third law holds true? ("horse pulls on wagon, wagon pulls on horse")
horse pushes on ground, ground pushes on horse wagon pushes on ground, ground pushes on wagon ground pushing on horse doesn't equal ground pushing on wagon
500
My weight is 1000 N on earth. What would my weight be on Mars if the acceleration is 3.7 m/s^2?
What is 380 N?
500
An 80 kg baseball player slides onto 3rd base. The coeffictent of the kinetic friction for the player on the ground is 0.70. His speed at the start of the slide is 8.23 m/s. How much distance is he sliding for?
Ffr=uFn=(0.70)(80x9.8)=-549N a=F/m=-549/80=-6.86 m/s^2 V^2=Vo^2+2ad 0=8.23^2+2(-6.86)d -67.7=-13.72d d=4.93m
500
1. Spoilers uses the following force on race cars. 2. What is its purpose. 3. What else could you do to achieve the same effect?
1. air friction 2. Keeps the car from lifting off the ground 3. Add more mass/weight