Download Forces Question Paper

Questions
Q1.
The diagram shows the forces acting on a car which is travelling along a flat straight road.
Forces also act on objects when they fall through the air.
There are two forces acting on this ball as it falls through the air.
The weight is shown on the diagram.
(i) Draw and label an arrow on the diagram to show the other force acting on the ball.
(2)
(ii) Use words from the box to complete the sentences.
(2)
balanced
changing
greater
smaller
zero
After a short time the ball falls at a steady speed.
The forces acting on the ball are now . . . . . . . . . . . . . . . . . . . . . . .
The acceleration of the ball is now . . . . . . . . . . . . . . . . . . . . . . .
Q2.
(a) Here is the velocity-time graph for a car for the first 20 s of a journey.
(i) Calculate the change in velocity of the car during the first 5 s.
(1)
..............................................................................................................................................
(iii) State the size of the resultant force between 10 s and 15 s
(1)
..............................................................................................................................................
Questions
Q1.
Forces and motion
(a) The diagram shows some of the forces acting on an airliner in flight.
The airliner is flying at a constant height above the ground.
Only two of the forces acting on the airliner are shown.
(i) Use words from the box to label the diagram.
(2)
thrust
drag
lift
weight
(ii) Draw another arrow on the diagram to show the friction forces acting on the airliner.
(1)
(iii) The airliner is accelerating.
Which of these statements is correct for the accelerating airliner?
Put a cross ( ) in the box next to your answer.
(1)
A the friction forces are zero
B the thrust is greater than the friction forces
C the thrust is smaller than the friction forces
D the thrust is the same size as the friction forces
Q2.
The diagram shows the forces acting on a car which is travelling along a flat straight road.
(i) The size of the resultant force on the car is 350 N.
In which direction is the resultant force acting?
Put a cross (
) in the box next to your answer.
(1)
A down ↓
B to the left ←
C to the right →
D up ↑
(ii) Complete the sentence by putting a cross (
The car is
) in the box next to your answer.
(1)
A
B
C
D
accelerating
decelerating
moving at a constant speed
not moving
Examiner's Report
Q1.
(i)
The majority of candidates showed the other force acting on the ball by an arrow pointing upwards. A
mark was given for the arrow being placed anywhere on the diagram but it should be vertical from the
same point as the weight. The labelling should be 'air resistance', 'upthrust' or 'drag'. 'Reaction' was not
accepted as both of the forces are acting on the same object.
Results Plus: Examiner Comments
1 mark was awarded, the arrow was not labelled.
Results Plus: Examiner Tip
Read the question carefully and make sure that all parts of the question are completed.
Results Plus: Examiner Comments
The arrow is correct so 1 mark was awarded but 'reaction' is not an acceptable
alternative to air resistance so this answer could not achieve both marks.
(ii)
Candidates must read the whole question to establish that the ball is moving at a steady speed.
As it is not accelerating or decelerating the forces are balanced.
Since the forces are balanced, there is no acceleration, ie the acceleration is zero.
Q2.
aiii
Candidates should be aware that if they are asked to state a value then a calculation is not
necessary. This question asked candidates to 'state the size' of the resultant force between 10s
and 15s. The graph shows that the car had a constant velocity during this time and so the
resultant force must be zero.
Results Plus: Examiner Comments
The answer should be simply 0.
Results Plus: Examiner Tip
You do not need to do a calculation if you are simply asked to 'state the size' of
something.
ai-ii
For the first part of this question (i), candidates needed to subtract the starting velocity (0) from
the velocity at 5s (8 m/s) to arrive at an answer of 8 m/s. Many candidates calculated the
acceleration in this part by finding the gradient of the line.
In the second part (ii), candidates needed to divide the change in velocity in part (i) by the time
taken (5s) to find the acceleration (1.6 m/s2). Provided that working was shown, examiners
allowed full credit for an error carried forward from (i) into (ii).
Although the answer to part (i) is incorrect, the candidate has carried on to use the value to
calculate acceleration and has shown the working. The examiner could clearly see that the
candidate knows how to find acceleration and awarded 2 marks for part (ii).
Results Plus: Examiner Comments
Candidates need to be clear about the difference between 'change in velocity' and 'rate
of change in velocity' (ie acceleration).
Results Plus: Examiner Tip
'Calculate' does not always mean that you have to multiply or divide. It can also mean
add or subtract.
b
This was a straightforward calculation for most candidates. The most common error seemed to
be incorrect use of the calculator by carrying out a division of 1200 by 0.8 to produce a result of
1500. As usual, candidates could score 1 mark if the substitution was correctly shown.
Results Plus: Examiner Comments
This clearly laid out response scored 2 marks.
A mark was given for substituting the correct values into the equation.
Results Plus: Examiner Comments
The expression 1200 Kg x 0.8 is correct for one mark.
Unfortunately the candidate seems to have used the divide function on the calculator
and so could not get the second mark.
Results Plus: Examiner Comments
The candidate may have made the same mistake and pressed divide rather than
multiply on the calculator. Unfortunately, there was no working shown and so no marks
were scored.
Results Plus: Examiner Tip
Always show your working.
c
Most candidates realised that the extra passengers and luggage would increase the overall mass
of the car. However, very many expressed this as an increase in weight rather than mass. This
seemed to lead them towards considering downwards forces on the road and, very often,
increase in friction. They then drew the conclusion that this would make the car stop more
quickly in an emergency. There was a widespread misunderstanding that it was friction between
the tyres and the road which was responsible for stopping the car when the brakes were applied.
It was surprising that a large number of candidates thought that a heavily loaded car could stop
more quickly than one with just the driver.
Candidates who correctly used the term 'increase in mass' very often went on to reason that the
car would take a longer time to come to halt. This was sometimes nicely expressed in terms of
momentum or kinetic energy and sometimes expressed in terms of forces and rate of change of
velocity.
It was sometimes difficult for the examiner to decide whether 'takes longer to stop' referred to a
longer time or a greater distance.
There were quite a few candidates who suggested that the passengers might distract the driver.
They often went on to give a good description of how this could affect overall stopping distance
by increasing the thinking distance. Examiners gave credit for this.
Results Plus: Examiner Comments
This answer makes a correct statement about the mass or weight increasing when the
car is fully loaded. This is a level 1 response. It then goes on to consider resistance and
forces pulling the car down to arrive at a conclusion that the car will stop quicker than
an unloaded car. This is incorrect and so cannot reach level 2. It scored only 2 marks.
Results Plus: Examiner Comments
The candidate links the increase in mass with taking 'longer to stop'. It is not clear
whether this is a longer time or a longer distance. The answer goes on to describe air
resistance and gravity which is not relevant in this situation. It then goes on to mention
resultant forces, but, once again, this is not in the correct context. The examiner ignored
the second and third sentences. The candidate eventually goes on to state that the
lighter car takes a shorter time to stop without mentioning distance. This is a good level
2 response but does not quite make the links clear enough to reach level 3. The quality
of written communication is appropriate. It scored 4 marks.
Results Plus: Examiner Comments
Although it not clear what force is being referred to, the answer makes very good points
about an increase in mass resulting in a longer time to stop and so a longer distance
travelled. This is a level 3 response. The quality of written communication is appropriate
for this level. It scored all 6 marks.
Q3.
This was a straightforward calculation for most candidates. The most common error seemed to
be incorrect use of the calculator by carrying out a division of 1200 by 0.8 to produce a result of
1500. As usual, candidates could score 1 mark if the substitution was correctly shown.
Results Plus: Examiner Comments
This clearly laid out response scored 2 marks.
A mark was given for substituting the correct values into the equation.
Results Plus: Examiner Comments
The expression 1200 Kg x 0.8 is correct for one mark.
Unfortunately the candidate seems to have used the divide function on the calculator
and so could not get the second mark.
Results Plus: Examiner Comments
The candidate may have made the same mistake and pressed divide rather than
multiply on the calculator. Unfortunately, there was no working shown and so no marks
were scored.
Results Plus: Examiner Tip
Always show your working.
Mark Scheme
Q1.
Answer
(i)
(ii)
Acceptable
answers
upward arrow on any
part of line vertical
(1) air resistance line from any point
(1)
on the diagram air
friction, upthrust,
drag Ignore any
downward arrow
labelled weight or
gravity
Balanced (1) Zero
(1)
Mark
Answer
Mark
(2)
(2)
Q2.
(a)(i)
(a)(ii)
(a)(iii)
(b)
8 – 0 (m/s)
substitution
8 / 5 (1) evaluation
(1)
1.6 (m/s2)
0
substitution
F = 1200 ×
0.8
(1)
evaluation
Acceptable
answers
8
ecf from (i) full marks
for correct answer
(or ecf) with no
working shown.
Nil / nothing / zero /
none
(no mark for no
response)
(1)
(2)
(1)
full marks for correct
answer with no
working shown.
(1)
(2)
960 (N)
QWC
*(c)
Indicative Content
Mark
an explanation
linking some of the
following points:
compared to a car
with just the driver, a
fully loaded car will
 have a greater
mass / be heavier
 greater kinetic
energy / momentum
 experience the
same braking force
(when brakes are
applied)
 require a greater
braking force (than
(6)
Level
1
0
1-2
available) to stop (in
the same distance)
 have a smaller
acceleration /
deceleration
 take a longer
time to come to rest
(from given speed)
 travel greater
distance in this time
 needs to do
more work with same
amount of force
 use of relevant
equations such as F
= ma, work done = F
×d
 consequence of
driver distractions
No rewardable content
 a limited explanation using one idea from
the indicative content eg fully loaded car is
heavier.
 in answer communicates ideas using
simple language and uses limited scientific
terminology
 spelling, punctuation and grammar are
used with limited accuracy
2
3-4
 a simple explanation which links ideas
from the indicative content eg it is heavier
and so it takes a longer distance to stop
 the answer communicates ideas
showing some evidence of clarity and
organisation and uses scientific terminology
appropriately
 spelling, punctuation and grammar are
used with some accuracy
3
5-6
 a detailed explanation which links
several ideas from the indicative content e.g.
It has more momentum and so it will take a
longer time to stop. This means that it will
travel a further distance. The answer
communicates ideas clearly and coherently
uses a range of scientific terminology
accurately
 spelling, punctuation and grammar are
used with few errors
Q3.
Answer
Acceptable
answers
substitution
F = 1200 ×
0.8
(1)
evaluation
Mark
full marks for correct
answer with no
working shown.
(1)
960 (N)
(2)