Difficult questions from 2016 HSC

[sidzeman]

Could someone explain the MC questions to me?

[Mymy409]

Hey!
So, in Q17, the solid line shows the path of the ball in a stationary lift. The only force acting on it is gravity.

The second time the ball is launched, it's when the lift is slowing down, not the whole duration of the lift going up.

B and D are clearly wrong; the path of the ball is much too drastic in B and it seems to be travelling at a constant velocity which shouldn't happen as there is gravity and g-forces involved. The lift is slowing down, so the ball shouldn't be 'pushed' downwards as it is in D.

As the lift is going upwards, it works against gravity making the ball more weightless. So the ball 'floats' a bit before heading down. Therefore, the answer is C. Sorry, probably not the best way to explain it, but I tried.

Q19:
So muons travel at close to the speed of light, therefore special relativity applies. Since we're talking about their lifetime and distance travelled, we know the qn is talking about time dilation and length contraction.

They have a lifetime of 2.2 microseconds at rest and distance travelled is 660m. This is what they experience as they travel at 0.9999c. They experience everything normally as it would be from their frame of reference. Therefore, A or C is the answer.

Scientists on Earth calculate their lifetime to be longer, as we see that time is going faster for them and hence slower for us. Therefore, the answer is A.

Sorry if these weren't great explanations! If anyone else has anything better, please add to this.

As for Q20, I'm stumped as well.

[Checkmate123]

You know that if DC is applied, due to the split-ring commutator, current will flow in one direction and give constant torque. 2 things happen when you switch to AC.
1. The direction of current flow changes
2. As a result of 1, since the magnetic field is produced by an electromagnet, the magnetic field also changes
Hence, you have a sort of a double negative situation. Whenever current flows in the opposite direction, the magnetic field also reverses and by Right hand palm rule, the net force aka torque remains in constant direction.

[arunasva]

Could someone explain the MC questions to me?

question 20 is B the RIGHT magnet is a SOUTH POLE the LEFT magnet is a north pole and CURRENT direction  is anti clocKwise in the motor


Use solenoid rule to find out which way the magnetic pole is

use right hand palm rule to figure out the motor or the 3 finger rule

[sidzeman]

Hey!
So, in Q17, the solid line shows the path of the ball in a stationary lift. The only force acting on it is gravity.

The second time the ball is launched, it's when the lift is slowing down, not the whole duration of the lift going up.

B and D are clearly wrong; the path of the ball is much too drastic in B and it seems to be travelling at a constant velocity which shouldn't happen as there is gravity and g-forces involved. The lift is slowing down, so the ball shouldn't be 'pushed' downwards as it is in D.

As the lift is going upwards, it works against gravity making the ball more weightless. So the ball 'floats' a bit before heading down. Therefore, the answer is C. Sorry, probably not the best way to explain it, but I tried.

Q19:
So muons travel at close to the speed of light, therefore special relativity applies. Since we're talking about their lifetime and distance travelled, we know the qn is talking about time dilation and length contraction.

They have a lifetime of 2.2 microseconds at rest and distance travelled is 660m. This is what they experience as they travel at 0.9999c. They experience everything normally as it would be from their frame of reference. Therefore, A or C is the answer.

Scientists on Earth calculate their lifetime to be longer, as we see that time is going faster for them and hence slower for us. Therefore, the answer is A.

Sorry if these weren't great explanations! If anyone else has anything better, please add to this.

As for Q20, I'm stumped as well.

Those explanations made perfect sense actually thank you (and everyone else who commented) so much!

[pikachu975]

Those explanations made perfect sense actually thank you (and everyone else who commented) so much!

Just another explanation for 17 if you want:

Since acceleration is down (it is decelerating) then we know the ball will move up, as seen by accelerating forward in the car and your body moves back due to inertia. This means its fall is slowed.