PHYSICS 231 Lecture 9: Revision. Remco Zegers Walk-in hour: Thursday 11:30-13:30 Helproom. The slides about friction are in lecture 8!!. TRIGONOMETRY. SOH-CAH-TOA: sin=opposite/hypotenuse cos=adjacent/hypotenuse tan=opposite/adjacent. Pythagorean theorem:. Units.
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Walk-in hour: Thursday 11:30-13:30
Vector operations in equations
length/magnitude of A: (Xa2+Ya2)
Parabolic motion: decompose x and y directions
=34 (hit the
=0 (hits the ground)
A snowball is launched horizontally from the top of a building
at v=12.7 m/s. If it lands 34 m away from the bottom, how high was the building?
13.3=31.8t so t=0.42s
A red ball is thrown upward with a velocity of 26.8 m/s.
A blue ball is dropped from a 13.3 m high building with
initial downward velocity of 5.00 m/s. At what time will
the balls be at the same height.
In first period: v(t)=v0+at=0+1.48·5.09=7.53 m/s
In 2nd period: v(t)=v0+at=7.53-1.91·2.96=1.88 m/s
A car starts at rest and travels for 5.09 s with uniform
acceleration of +1.48 m/s2. The driver then brakes, causing
uniform acceleration of -1.91 m/s2. If the brakes are applied
for 2.96 s how fast is the car going after that?
Due to tide: 3000 N 0 N
Due to wind: 6000cos(135)=-4243 6000sin(135)=+4243
Sum: -1243 N 4243 N
Magnitude of resulting force:
1060 (calc: -730, add 1800)
F=ma so a=F/m=4421/2000=2.21 m/s2
A 2000 kg sailboat is pushed by the tide of the sea with a force of 3000 N to the East. Because of the wind in its sail
it feels a force of 6000 N toward to North-West direction.
What is the magnitude and direction of the acceleration?
left rope Tsin(45) Tcos(45)
right rope -Tsin(45) Tcos(45)
gravity 0 -1*9.81
Sum: 0 2Tcos(45)-9.81
Object is stationary, so:
2Tcos(45)-9.81=0 so, T=6.9 N
A mass of 1 kg is hanging from a rope as shown in the figure.
If the angle between the 2 supporting wires is 90 degrees,
what is the tension in each rope?