HSC Physics Marathon 2017 (2 Viewers)

[InteGrand]

Quote the formulas of motion (should be obvious) set y as -50 to get t --> sub into the x-motion.

Note that in your answer both solutions are positive, so you would need to decide (with justification!) which solution is right.

 

[WildestDreams]

How do you guys know all this stuff? You haven't even started learning HSC content yet!

 

[eyeseeyou]

How do you guys know all this stuff? You haven't even started learning HSC content yet!

We self learn it

 

[trecex1]

Note that in your answer both solutions are positive, so you would need to decide (with justification!) which solution is right.

Revised answer if I didn't make any more algebraic mistakes.
Edit: The value with the + (first one) should be omitted as the value of T will be negative. I.e the sound will take longer to reach her from the bottom of the well than the time it takes for the stone to fall and the sound to reach her(?!), which is impossible.

 

[eyeseeyou]

A stone is thrown vertically upwards with a velocity of 29.4 m/s from the edge of a cliff 78.4 m high. The stone falls so that it just misses the edge of the cliff and falls to the ground at the foot of the cliff. Determine the time taken by the stone to reach the ground. Assume that the acceleration due to gravity is 9.8 ms-2

 

[jazz519]

A stone is thrown vertically upwards with a velocity of 29.4 m/s from the edge of a cliff 78.4 m high. The stone falls so that it just misses the edge of the cliff and falls to the ground at the foot of the cliff. Determine the time taken by the stone to reach the ground. Assume that the acceleration due to gravity is 9.8 ms-2

https://postimg.org/image/d0zyhtyp9/

 

[eyeseeyou]

Discuss the g-forces astronauts experience during the launch of a multi stage rocket and assess measures taken to minimize them. (7 marks)

 

[Commando007]

Jathu u nerd
it's Uy NOT Uu

 

[UnbiasedProductivity]

And about the link that eyeseeyou posted, remember that if you do the option Astrophysics, you need to know most content from the cosmic engine.

Actualyyyy, I didn't bother remembering anything from Prelim and I'm doing great in Astro.
I guess it's iseful to remember some concepts like H-R Diagram and stars. But majority of it is new content. That's just my 2 cents.

 

[Commando007]

Determine the gravitational force between a 77.5 kg astronaut and Earth when he is standing on the ground. Calculate the change in gravitational force when the astronaut is inside a satellite orbiting the Earth at an altitude of 685 km. The radius of the Earth is 6380 km and the mass of the earth is 5.97*10^24 kg. [4 marks]

 

[Green Yoda]

F(G on surface)= (6.67x10^-11 x 77.5 x 5.97x10^24)/((6380x10^3)^2)=758.16N
F(G inside satellite) =(6.67x10^-11 x 77.5 x 5.97x10^24)/((6380x10^3 +685x10^3)^2)=618.27N
ΔF(G)= 618.27-758.16=-139.89N
=138.89N opposite the direction of the center of Earth

 

[Commando007]

F(G on surface)= (6.67x10^-11 x 77.5 x 5.97x10^24)/((6380x10^3)^2)=758.16N
F(G inside satellite) =(6.67x10^-11 x 77.5 x 5.97x10^24)/((6380x10^3 +685x10^3)^2)=618.27N
ΔF(G)= 618.27-758.16=-139.89N
=138.89N opposite the direction of the center of Earth

not a big mistake but it's 138.89 in the second last step

 

[Green Yoda]

not a big mistake but it's 138.89 in the second last step

I still get 139.89

 

[Green Yoda]

Three moons X, Y and Z are in orbit around the same planet. The moons have identical orbital speeds and masses of M, 9M and 25M respectively. Determine the ratio of their orbital radii and justify your answer.

 

[Commando007]

I still get 139.89

my bad
didnt read it carefully

 

[Commando007]

Three moons X, Y and Z are in orbit around the same planet. The moons have identical orbital speeds and masses of M, 9M and 25M respectively. Determine the ratio of their orbital radii and justify your answer.

The ratio is just 1:1:1 as orbital radii --> identical for all three moons (since the orbital speed and orbital does not depend on the mass).
When Fc = Fg
where Fc = (mv^2)/2 -------- and Fg = (GmMp)/r^2 )where Mp is the mass of the planet)

ending up with r = (GMp)v^2 (masses cancel out so the orbital speed and orbital radii does not depend on the mass) and r is constant in this case
THEREFORE the ratio is 1:1:1

 

[dragon658]

So I'm a bit stumped on how to find the launch speed and angle of launch from the horizontal. I'm given the Horizontal component which is 30 ms^-1 and the vertical component which is 80 ms^-1.

 

[Green Yoda]

So I'm a bit stumped on how to find the launch speed and angle of launch from the horizontal. I'm given the Horizontal component which is 30 ms^-1 and the vertical component which is 80 ms^-1.

u(y)=80m/s
u(x)=30m/s

by Pythagoras theorem
∴|u|=√(u(y)^2)+(u(x)^2))
∴|u|=√80^2+30^2
∴|u|≈85.44m/s
θ (below horizontal) = tan^-1(u(y)/u(x))
∴θ=tan^-1(80/30)
∴θ≈69°

 

[Commando007]

A golf ball was smashed at 25ms^-1 and at a angle of 40 degrees
a) find the total time it took for the ball to bounce (2 marks)
b) find range (2 marks)

 

[trecex1]

A golf ball was smashed at 25ms^-1 and at a angle of 40 degrees
a) find the total time it took for the ball to bounce (2 marks)
b) find range (2 marks)

y=25tsin40-4.9t^2
x= 25tcos40
t= 3.28s

Range = 62.8m