VCE Physics Question Thread!

[Bestie]

mass of 10kg is place on a plane inclined at 45 degrees to the horizontal and allowed to slide down the plane. WHat is the accleration of mass if the frictional force opposing motion is 3.2 N?

help please

[allstar]

thank you conic

but what happens if it was initially constant velocity and then accelerate in the opposite direction, is the gradient of acceleration positive or negative in this case?

[Conic]

It's the same situation, but the gradient will start off at 0 then change when the object starts accelerating.

[knightrider]

how would you do this question?

A removalist is loading five boxes onto a truck.
Each has a mass of 10 kg and a height of 30 cm. The
tray of the truck is 1.5 m above the ground and the
removalist is placing each box on top of the previous
one.

What is the total work done on the boxes in lifting
all the boxes onto the truck as described?

[JHardwickVCE]

Work (W) = Force (F) * Displacement (x)

As we are lifting boxes, the force is made up by the weight force = mg
Hence, each box, when lifted, has a force of (10)(10)=100N pulling it down.

For the first box:
x=1.5m
W=(100)(1.5) = 150N

You will have to lift each box an extra 0.3m

Total work done = (100)(1.5+1.8+2.1+2.4+2.7) = (100)(10.5) = 1050N = 1.1*10^3 N

[lzxnl]

Work (W) = Force (F) * Displacement (x)

As we are lifting boxes, the force is made up by the weight force = mg
Hence, each box, when lifted, has a force of (10)(10)=100N pulling it down.

For the first box:
x=1.5m
W=(100)(1.5) = 150N

You will have to lift each box an extra 0.3m

Total work done = (100)(1.5+1.8+2.1+2.4+2.7) = (100)(10.5) = 1050N = 1.1*10^3 N

Your answer is correct, but be careful of the working.
For instance, if you were to actually try to exert a force equal to the weight force on the box, the net force on the box would be zero. Problem. In reality, we pull up with a greater force than the weight force to get the box moving, and then we reduce the force when we want to slow it down, so the force isn't constant. W = Fx only works for constant forces.

What you should actually do is note that the kinetic energy at the beginning and the end is zero, so the work done is the change in gravitational potential energy. The working out is the same, the reasoning isn't.

[knightrider]

Work (W) = Force (F) * Displacement (x)

As we are lifting boxes, the force is made up by the weight force = mg
Hence, each box, when lifted, has a force of (10)(10)=100N pulling it down.

For the first box:
x=1.5m
W=(100)(1.5) = 150N

You will have to lift each box an extra 0.3m

Total work done = (100)(1.5+1.8+2.1+2.4+2.7) = (100)(10.5) = 1050N = 1.1*10^3 N

Your answer is correct, but be careful of the working.
For instance, if you were to actually try to exert a force equal to the weight force on the box, the net force on the box would be zero. Problem. In reality, we pull up with a greater force than the weight force to get the box moving, and then we reduce the force when we want to slow it down, so the force isn't constant. W = Fx only works for constant forces.

What you should actually do is note that the kinetic energy at the beginning and the end is zero, so the work done is the change in gravitational potential energy. The working out is the same, the reasoning isn't.

Thx lzxnl and jhardwickvce

But remember jhardwickvce that work is measured in joules or newton metres
in your working out you wrote newtons at the end

By the way jhardwickvce and lzxnl how different is physics 1/2 to 3/4 physics and how are you guys finding it/found it

[Phenomenol]

Thx lzxnl and jhardwickvce

But remember jhardwickvce that work is measured in joules or newton metres
in your working out you wrote newtons at the end

By the way jhardwickvce and lzxnl how different is physics 1/2 to 3/4 physics and how are you guys finding it/found it

I know I'm not jhardwickvce nor lzxnl but I hope you don't mind me answering this question.

Motion in 3/4 builds upon what was learnt in 1/2 very well. Some new concepts involve circular motion, more intricate block/ramp systems and newtons's law of gravity.

Electricity involved familiar stuff too. Some additions included diodes, thermistors, photodiodes, light-dependent resistors in circuits. A common question is to figure out where to place a cooling/heating element in a circuit.

Light is a different story entirely (at least from what I learned in 1/2). In 1/2 we did a lot of ray tracing and calculations based on focal lengths of lenses/mirrors, but in 3/4 the content shifted towards wave/particle duality of light and the experiments that proved such light properties (photoelectric effect, interference patterns). I found this topic the driest and most repetitive.

Electromagnetism was not something we were taught in 1/2 so concepts like flux and field took a bit of time to get comfortable with, but otherwise it's fine.

[knightrider]

I know I'm not jhardwickvce nor lzxnl but I hope you don't mind me answering this question.

Motion in 3/4 builds upon what was learnt in 1/2 very well. Some new concepts involve circular motion, more intricate block/ramp systems and newtons's law of gravity.

Electricity involved familiar stuff too. Some additions included diodes, thermistors, photodiodes, light-dependent resistors in circuits. A common question is to figure out where to place a cooling/heating element in a circuit.

Light is a different story entirely (at least from what I learned in 1/2). In 1/2 we did a lot of ray tracing and calculations based on focal lengths of lenses/mirrors, but in 3/4 the content shifted towards wave/particle duality of light and the experiments that proved such light properties (photoelectric effect, interference patterns). I found this topic the driest and most repetitive.

Electromagnetism was not something we were taught in 1/2 so concepts like flux and field took a bit of time to get comfortable with, but otherwise it's fine.

Thankyou Phenomenol

[knightrider]

How would you do this question?

A rope that is at 35° to the horizontal is used to pull a
10.0 kg crate across a rough floor. The crate is initially
at rest and is dragged for a distance of 4.00 m. The
tension in the rope is 60.0 N and the frictional force
opposing the motion is 10.0 N.

Determine the energy lost from the system as heat
and sound due to the frictional force.

[allstar]

The maximum rate at which a bus can accelerate or decelerate is 2 m/s2. It has a
maximum speed of 60 km/h. Find the shortest time the bus can take to travel between
two bus stops 1 km apart on a straight stretch of road.

please?

[Brunette15]

Can someone please help me calculate this question for structures and materials:

A winch uses a steel cable to lift a large piece of machinery
from a loading dock. While supporting this load the length
of the steel cable increases to 1.001 times its original
value. What is the tensile strain on the cable when
supporting this load? Express your answer as a
percentage

[Rishi97]

Can someone please help me calculate this question for structures and materials:

A winch uses a steel cable to lift a large piece of machinery
from a loading dock. While supporting this load the length
of the steel cable increases to 1.001 times its original
value. What is the tensile strain on the cable when
supporting this load? Express your answer as a
percentage

Hey
Ok when I did this question, I just made up random numbers to get an idea of what the question is trying to say.
Lets say that the original length is 5m
When the cable increases to 1.001 times its original length, then 5x1.001 = 5.005
That means that the change in length is 0.005
Sub into the strain=change in length/ original length and you should get an answer of 0.001
Since the answer says to give as a percentage, 0.001 x 100 = 0.1%
That should be right

[qwerty04]

2 quick questions  (i have a very basic understanding of the photoelectric effect so far)

Why is a vacuum needed in a photocell?


Why do photoelectric cells need to be stored in a dark space?

[Brunette15]

Is the yield strength the same as the elastic limit of a material? If not what is the difference?