Q&A - PSLE Science

[atutor2001]

Sun_2010:

Hi,


Just wanted to check on this question from 2009 Rosyth SA2 p6


http://www.postimage.org/image.php?v=PqaRCVS

The answer given is 1
I think it should be B and C ( there is no such option)

:?:

Allow me to join in the fun. My understanding is that :

1. The PE will be the same if the car is released from the same height, regardless of the slope.

2. Though the PE is the same, the force exerted by the car on the ball depends on the slope. (The steeper the slope is, the bigger will be the force exerted by the car on the ball because the force component parallel to the ramp is longer - this is not in Pr syllabus.)

3. The KE of the car at the bottom of the ramp, depends on its PE at the starting position and also the slope of the ramp.

4. The distance moved by the ball depends on the KE of the car at the bottom of the ramp, which is dependent on its PE at the starting position and the slope of the ramp. Therefore, the PE must be kept constant in order to have a fair test.

5. Definition of \"position the car is released\" - should be relative to its location on the ramp.

My answers are :

a.) Option 1 (A & C) can be the answer because with \"A\" the height (no. of books) remaining unchanged, we can change the slope by using different lengths for the ramps. The shorter the ramp, the steeper will be the slope. The car must be released from the same position \"C\" i.e. we can fixed it at the top END of the ramp.

b.) B & C CANNOT be the answer because with \"B\" the length of the ramp remaining unchanged, in order to change the slope, we need to change the height (no. of books). Changing the height would mean changing the PE of the car, (PE must be constant), unless we change \"C\", the starting position of the car which contradicts with \"C\", i.e. position remaining unchanged.

c.) Option 2 (A, B, C) also cannot be the answer because though we can increase the slope of the same ramp by pushing the bottom of the \"ruler\" nearer to the book, the car must be released from different position on the ramp so that its height (PE) above ground remainds the same. However, this will contradict with \"C\", \"the position the car is released\" being unchanged.

In conclusion, the answer is option 1.

[Dharma]

Tang:

Dharma:

[quote=\"Sun_2010\"]Hi,


Just wanted to check on this question from 2009 Rosyth SA2 p6


http://www.postimage.org/image.php?v=PqaRCVS

The answer given is 1
I think it should be B and C ( there is no such option)

:?:

Hi,

Think that the clue is given in the question \" ... The FORCE of the toy car rolling down ...\".

The force acting on the toy car are gravitational and frictional. Frictional is irrelevant here as the ramp used is the same.

So, the steeper the slope, the greater the gravitational force acting on the toy car.

[I thought gravitational force is dependent on the mass of thee toy car and has nothing to do the slope or its height.]

To make the slope steeper, we should not increase the number of books cause the distance the ball moves will be influenced by the change in energy (GPE to KE) besides the change in the gravitational force in the toy
car.

If we do not increase the number of books we must also make sure that the point where the toy car is released is on the ramp just above the highest
book.

Agree with the given answer (1)

Hello,

See highlight in blue.[/b][/quote]Gravitational force is dependent on mass of the object, m and the acceleration of the object under gravitational pull, g. The gravitational force acts vertically downwards.

Remember... Our toy cat is placed on a slope ;in this case a ramp. So, if you hold the toy car and just release without applying any force; the net force acting on the toy car I'd likely to be downwards unless the frictional resistance of the ramp and the wheels of the toy car is so high that it prevents the car moving down the ramp.

What is the force that causes the toy car to move down? It is the gravitational force. The gravitational force acting along the slope will be lower than that when it acts vertically downwards. As the slope becomes less and less steep, the gravitational force on the toy car will become smaller and smaller. If the inclination of hhe ramp is zero, then gravitational force on the toy car becomes zero and the toy car will not move on it's own unless an external force is applied on it.

[MOE Hater]

Dharma:

Tang:

[quote=\"Dharma\"]
Hi,

Think that the clue is given in the question \" ... The FORCE of the toy car rolling down ...\".

The force acting on the toy car are gravitational and frictional. Frictional is irrelevant here as the ramp used is the same.

So, the steeper the slope, the greater the gravitational force acting on the toy car.

[I thought gravitational force is dependent on the mass of thee toy car and has nothing to do the slope or its height.]

To make the slope steeper, we should not increase the number of books cause the distance the ball moves will be influenced by the change in energy (GPE to KE) besides the change in the gravitational force in the toy
car.

If we do not increase the number of books we must also make sure that the point where the toy car is released is on the ramp just above the highest
book.

Agree with the given answer (1)

Hello,

See highlight in blue.[/b]

Gravitational force is dependent on mass of the object, m and the acceleration of the object under gravitational pull, g. The gravitational force acts vertically downwards.

Remember... Our toy cat is placed on a slope ;in this case a ramp. So, if you hold the toy car and just release without applying any force; the net force acting on the toy car I'd likely to be downwards unless the frictional resistance of the ramp and the wheels of the toy car is so high that it prevents the car moving down the ramp.

What is the force that causes the toy car to move down? It is the gravitational force. The gravitational force acting along the slope will be lower than that when it acts vertically downwards. As the slope becomes less and less steep, the gravitational force on the toy car will become smaller and smaller. If the inclination of hhe ramp is zero, then gravitational force on the toy car becomes zero and the toy car will not move on it's own unless an external force is applied on it.[/quote]
I thought that all matter in the universe exerts a gravitational force on all other matter regardless of their location. I that case how can the gravitational force acting on the car ever become zero.

[Dharma]

MOE Hater:

Dharma:

[quote=\"Tang\"]
Hello,

See highlight in blue.[/b]

Gravitational force is dependent on mass of the object, m and the acceleration of the object under gravitational pull, g. The gravitational force acts vertically downwards.

Remember... Our toy cat is placed on a slope ;in this case a ramp. So, if you hold the toy car and just release without applying any force; the net force acting on the toy car I'd likely to be downwards unless the frictional resistance of the ramp and the wheels of the toy car is so high that it prevents the car moving down the ramp.

What is the force that causes the toy car to move down? It is the gravitational force. The gravitational force acting along the slope will be lower than that when it acts vertically downwards. As the slope becomes
less and less steep, the gravitational force on the toy car will become smaller and smaller. If the inclination of hhe ramp is zero, then gravitational force on the toy car becomes zero and the toy car will not move on it's own unless an external force is applied on it.

I thought that all matter in the universe exerts a gravitational force on all other matter regardless of their location. I that case how can the gravitational force acting on the car ever become zero.[/quote]Hi Moe Hater,

What I meant was when ramp's inclination is reduced to the extent such it it becomes horizontal, the component of the gravitational force acting on the toy car along the ramp becomes zero. Thus the net force on the toy car will be zero and the toy car will not move.

[tianzhu]

Hi


In answering this question, we need to apply the concept of fair testing.
From PSLE Science Guide (MC), we learned about the importance of a fair test. We should change only the variable we are testing.

Amanda carry out an experiment to show how the slope of a ramp affected the distance the ball was moved by the force of the toy car rolling down the slope. We are supposed to measure the distance moved by the ball. This distance varies due to the strength (magnitude) of the component of the gravitational force acting on the car which is parallel to the ramp. Hence, it cannot be a constant which means option (D) is out .This effectively rules out (3) and (4)

Now let us look at (2) ------ If we change the height of the book, we change the height and slope of the ramp, therefore the experiment is not a fair one. Hence (2) is out.
To ensure a fair test, we need to keep the height of the ramp and position of the toy car constant. In this experiment, we change the length of the ramp to vary the slope.

Therefore, the answer given in the WS, option (1) is a reasonable answer.

Best wishes

[tianzhu]

Hi


If a child wishes to find out more about why there is a stronger force acting on the toy car on a steeper slope, I’ve prepared two slides which may be of some help.

First let us recap some of the facts learned under the topic of Forces in Upper Primary Science.

In primary science, students learned that a force is any push or pull. Force is needed to provide motion, change direction or speed, and to stop. Under the topic on Forces, they learned about Friction/Frictional Force, Elastic Spring force, Magnetic Force and Gravity/Gravitational Force.

From their experience in riding bicycles, children know that it’s easier to move down a steeper slope. You can move faster without much pedalling, due of gravity. Those who are privileged enough to enjoy skiing during the winter holidays will certainly remember those exciting moments.

In this experiment, the toy car rolls down the slope due to gravity. The steeper the slope, the greater is the force parallel to the ramp, Ft. The distance moved by the ball depends on the magnitude (strength) of Ft. (To be learned in higher learning)

http://farm5.static.flickr.com/4098/4789796416_2952cc0f7d_b.jpg\">
http://farm5.static.flickr.com/4114/4789796470_d5a0d59f9c_b.jpg\">

Best wishes

[underthesea]

tianzhu:

Hi


In answering this question, we need to apply the concept of fair testing.
From PSLE Science Guide (MC), we learned about the importance of a fair test. We should change only the variable we are testing.

Amanda carry out an experiment to show how the slope of a ramp affected the distance the ball was moved by the force of the toy car rolling down the slope. We are supposed to measure the distance moved by the ball. This distance varies due to the strength (magnitude) of the component of the gravitational force acting on the car which is parallel to the ramp. Hence, it cannot be a constant which means option (D) is out .This effectively rules out (3) and (4)

Now let us look at (2) ------ If we change the height of the book, we change the height and slope of the ramp, therefore the experiment is not a fair one. Hence (2) is out.
To ensure a fair test, we need to keep the height of the ramp and position of the toy car constant. In this experiment, we change the length of the ramp to vary the slope.

Therefore, the answer given in the WS, option (1) is a reasonable answer.

Best wishes

Hi,
I thought the question say \"Which of the following variables must she keep the same in order to have a fair test?\"

I don' understand why option (2) - length of the ramp is not part of the answer?

[happyluckymom]

Can you pls confirm the answer again for the direction of frictional force if the wheels of a car are moving in a certain direction?

[happyluckymom]

Also need to the answer for this question:

the moe the body temperature, the higher is the heart rate. Explain why such relationship occurs.

[Nebbermind]

happyluckymom:

Can you pls confirm the answer again for the direction of frictional force if the wheels of a car are moving in a certain direction?

http://webphysics.davidson.edu/faculty/dmb/py430/friction/idealroll1.gif\">