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A 20kg car moving 5m/s to the right crashes into a 45kg truck moving 10m/s to the left. Afterwards the truck is moving 4m/s to the right. Which direction and how fast is the car moving? Back 20kg*5m/s + 45kg(-10m/s) = 45kg*4m/s + 20kg*v 100kg*m/s – 450kg*m/s = 180kg*m/s + 20kg*v -350kg*m/s = 180kg*m/s + 20kg*v -530kg*m/s = 20kg*v V = (-530kg*m/s)/20kg = -26.5m/sTRANSCRIPT
Final Jeopardy Question
Momentum
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Energy
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Electricity
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A 20kg car moving 5m/s to the right crashes into a 45kg truck moving 10m/s to the left. Afterwards the truck is moving 4m/s to the right. Which direction and how fast is the car moving?
Back
20kg*5m/s + 45kg(-10m/s) = 45kg*4m/s + 20kg*v100kg*m/s – 450kg*m/s = 180kg*m/s + 20kg*v-350kg*m/s = 180kg*m/s + 20kg*v-530kg*m/s = 20kg*vV = (-530kg*m/s)/20kg = -26.5m/s
If a 20kg truck moving 15m/s to the right crashes into a 5kg car moving 20m/s to the left and they stick together, which direction and how quickly do they move?
20kg*15m/s + 5kg(-20m/s) = (20kg + 5kg) v300 kg*m/s – 100 kg*m/s = 25kg * v200 kg*m/s = 25kg*vV = 8 m/s to the right
Back
A 30kg truck is moving 5m/s to the right when it crashes into a 10kg car at rest. If the car moves 10m/s to the right, which direction and how fast does the truck move?30kg*5m/s = 30kg*v + 10kg*10m/s150kg*m/s = 30kg*v + 100kg*m/s50kg*m/s = 30kg*vV = 1.6m/s
Back
20kg*4m/s = 5kg*v80kg*m/s = 5kg*v
v=16m/s
A 20kg truck moving 4m/s crashes into a 5kg car at rest. If the truck stops, how fast does the car move?
Back
How much momentum does a 35kg car moving 14m/s have?
35kg*14m/s = 490 kg*m/s
Back
If a 20kg ball is compressed 4m in a spring (k=1000N/m) and released, how
fast will it move when it is 5m in the air? •SPE before = ½ 1000N/m * (4m)2
=500N/m*16m2 = 8000J Total Energy After = 8000J
GPE + KE after = 8000J20kg*10m/s/s*5m + 1/2*20kg*v2 =8000J
1000J + 10kg*v2 = 8000JV2 = 700m2/s2; v = sqrt 700 m/s Back
If a 10kg ball is moving 5m/s down when it is 10m high, how far will it compress a spring (k=200N/m) if 225J are lost as friction KE+ GPE - Friction → SPE1/2*10kg*(5m/s)2 + 10kg*10m/s/s*10m -
225J = SPE
125J + 1000J -225J =1/2(200N/m)x2
900J= 100N/m *x2
9m2 = x2; x=3m Back
How much force is required to stop a 10kg carMoving 4m/s in 4m
W=ΔKE; KE = ½ *10kg(4m/s)2
W = 80J = F*4mF=20N
Back
How fast would a 10kg sled on top of a 8m hill move when it reaches the bottom?
GPE → KE10kg*10m/s/s*8m → ½ 10kg v2
800J → 5kg * v2
160m2/s2--> v2
v=sqrt 160 m/s Back
How much kinetic energy does a 20kg car moving15m/s have?
½ 20kg*(15m/s)2 = 2250J
Back
A 75kg man is accelerating down 2m/s/sOn an elevator. What will a scale say he weighs?
Net force = 75kg*2m/s/s = 150N downFg = 75kg*10m/s/s = 750N downF up = 600N = reading on scale
Back
A 10kg object is being pulled by a spring (k=100N/m) that is causing it to accelerate up at 5m/s/s. How far is the spring stretched?Fnet= 5m/s/s*10kg = 50N up
Fdown = 100N, Fup = 150N100N/m * x = 150Nx=1.5m
Back
Fup =800N, Fdown =500N, net force = 300N upA=Fnet/m = 300N/50kg = 6m/s/s up
A 50kg person riding an elevator is on a scale.It says he weighs 800N. Which direction areThey accelerating and at what rate
Back
A 20kg object is hanging from a spring(k=20N/m). How far does it stretch?
Fdown=200N, Fup =200n200N = 20N/m * xX=10m
Back
Draw a free body diagram of a 100kg car driving 10m/s if there is 100N worth of friction.
Fup+down = 1000NFleft+right = 100N
Back
No, they are both positively charged
An atom with 8 protons, 7neutrons and 7 electrons is near an atom with 9 protons, 9 neutrons and 7 electrons. Are they attracted to each other?
Back
Draw an atom. Label the protons, neutrons and electrons
Back
An object with charge -6 is near an object with charge +2. What are their final charges and why?
-2,-2. 4 electrons flow
Back
180N * 1/9 = 20N
The electric force between two objects is 180N. If they are 3x as far apart, what is the force?
Back
What part of the atom carries negative charge? Positive charge?
Electrons, protons
Back
Identify as many units as you can (include what variable they go with) 100pts/unit
Distance-m Voltage - voltsVelocity –m/s Current - ampsAcceleration-m/s/s Wattage- wattsTime-s Charge - coulombsForce –N Spring Cons. - N/mEnergy – JMomentum – kg*m/s Back