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Assignment 2
Introduction
Aims
In this assignment you will answer questions based on the contents of Section 2 of the course. You will: ?? answer multiple-choice questions
?? describe practical situations and interpret measurements ?? solve problems in mechanics, using the methods taught in Section 2, using the equations on the data sheet.
These are the question types that are used in the A level examination papers.
The assessment objectives for the A level are to: ?? demonstrate knowledge and understanding of scientific ideas,
processes, techniques and procedures
?? apply knowledge and understanding of scientific ideas,
processes, techniques and procedures:
?? in a theoretical context ?? in a practical context ?? when handling qualitative data ?? when handling quantitative data
?? analyse, interpret and evaluate scientific information, ideas and evidence, including in relation to issues, to: ?? make judgements and reach conclusions ?? develop and refine practical design and procedures.
Your tutor will assess the following aspects of your work: ?? your application of appropriate physical principles ?? your use of appropriate equations ?? the accuracy of your calculations ?? your use of appropriate units.
An error in calculation in one step of a question will not normally lead to a loss of marks in subsequent calculations, provided the principles are applied correctly and your answers are consistent with the figures you have used.
Are you ready to do this assignment?
Before you start this assignment, make sure that you have done the quizzes and most of the practice exam questions in each of Chapters 3 to 6 of the textbook.
You should also do the pre-assignment quiz in Section 2 to check your understanding of what we have covered in this section.
In addition to the usual writing materials (or computer) you will need a sharp pencil, ruler and protractor, graph paper and a calculator.
What to do
Answer all the questions. If you get stuck on a question, make sure that you show your tutor how far you got, and say how you think you might tackle the rest of it.
In calculations, use g = 9.81 m s–2 for the acceleration of free fall, unless told otherwise.
1 Which of these statements is correct? Newton’s third law pairs of forces:
(a) can act at an angle to one another
(b) act on the same body
(c) act on different bodies
(d) can act in the same direction as one another (1 mark)
2 Which of the following is a unit of momentum?
(a) kg m s
(b) kg m s–2
(c) kg m s-1
(d) kg m2 s–2 (1 mark)
3 A body is raised from the floor to the top of a table. Which of the following graphs could represent the potential energy plotted as a function of height?
Figure 1
%\$ \$ \$ \$ \$ \$ L\$ \$ \$
\$

-\$ \$ \$ \$ \$ \$ N\$

\$
(1 mark)
4 Choose one option from Table 1 to show the resultant F of the two forces in Figure 2 (which are not drawn to scale):
Figure 2
?\$E\$

/9\$E\$
Table 1
Choice Value of F/N Angle ?
(a) 12 Tan–1 (5/12)
(b) 13 Sin–1 (5/12)
(c) 12 Cos–1 (5/13)
(d) 13 Cos–1 (12/13)
(1 mark)
5 What can be calculated from the area under a velocity/time graph?
(a) The acceleration
(b) The displacement
(c) The average velocity
(d) The distance travelled
(1 mark)
6 A gardener is pulling a heavy garden roller across a lawn. She exerts a force F on the handle, which is inclined at an angle ? to the ground, as shown. She pulls the roller a distance s along the level ground.
Figure 3
What is the work done by the force F?
(a) F cos ? multiplied by s
(b) F multiplied by s
(c) F sin ? multiplied by s
(d) zero (1 mark)
7 A mass of 1500 kg is raised 2.2 m in 8 s. What is the useful power expended by the crane?
(a) 410 W
(b) 4.0 kW
(c) 259 kW
(d) 836 W (1 mark)
8 A motorist is travelling down a country road at 27 m s–1 (which is the current speed limit). He comes over the brow of the hill and sees a tree has fallen across the road 100 m ahead of him. He was adjusting the volume of his radio at the time, so takes 1 second to react and apply the brakes. The brakes stop the car in a further 6 seconds.
(a) Draw a speed/time graph for this motorist starting at the beginning of his reaction time until the car comes to rest.
(4 marks)
(b) Use the graph to calculate the distance he travels from the beginning of his reaction time until the car comes to rest
(4 marks)
(c) Does he hit the tree? (1 mark)
(d) Calculate the acceleration from the instant the brakes are
applied to the moment the car comes to rest
(2 marks)
9 A girl is standing on a platform above the ground and throws a ball vertically upwards, with an initial velocity of 5 m s–1. It rises to a maximum height and then falls to earth. When she releases the ball it is 10 m above the ground as in the diagram:
Figure 4
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Calculate:
(a) the maximum height it reaches, relative to the ground
(2 marks)
(b) the velocity of the ball when it hits the ground (2 marks)
(c) the total time of flight (4 marks)
10 A cannon from the Napoleonic wars was able to launch cannon balls at a velocity of 540 m s–1. The cannon is fired at the top of a cliff with the barrel in the horizontal position.
(a) Neglecting air resistance, what is the range of the cannon ball, to the point where it hits the water 100 m below?
(4 marks)
(b) Calculate the initial horizontal component of the momentum of the cannon ball, if it has a mass of 5.44 kg. (2 marks)
(c) If the cannon has a mass of 5000 kg and is on a trolley on the horizontal surface, what is its initial recoil velocity?
(2 marks)
11 This question concerns Core Practical 1 Measuring the acceleration of free fall.
(a) Please submit the report of your experiment to calculate the acceleration due to gravity. Remember to record your apparatus, your method and the raw data (in tables, with
units). If you did not do this experiment, please describe the key features of the school experiment.
(5 marks)
Compile a table of the distance fallen versus the time taken for the object to fall that distance. Use your data if you can, but if you were not able to conduct the experiment, please use the data in Table 2:
Table 2
Distance fallen s /m Time taken t/s
0.52 0.33
0.67 0.38
0.89 0.43
1.04 0.46
1.15 0.48
The governing equation is: 21gt2
(b) Plot a graph of s versus t2. (4 marks)
(c) Find the slope of this line, and hence the value of the
acceleration of free fall, g. (4 marks)
(d) How many significant figures are appropriate for the
12 An athlete is performing curls, which consists of holding a weight of 50 N in the hand and bringing the arm from 45o below the horizontal to 45o above the horizontal. The biceps (thick arrow) exerts a force at 75o to the lower arm.
A schematic diagram of the arm in the mid position is shown in the diagram:
Figure 5
The weight of the arm, 20 N acts midway between the elbow and the load in the hand.
Calculate the force F in the biceps when the forearm is in the
horizontal position shown. (4 marks)
13 A block of weight 20 N is resting on a frictionless surface, which is inclined at 45º to the horizontal. It is prevented from sliding down the surface by a rope which is parallel to the surface, as shown in the diagram.
Figure 6
(a) Draw a free body diagram of the forces acting on the block
(2 marks)
(b) By doing a scale drawing, resolve the 20 N downwards force into two components, one parallel to the slope and one
perpendicular to the slope. (2 marks)
(c) Measure the drawing and deduce the magnitude of these
two component force (2 marks)
(d) Hence deduce the values of R and T (2 marks)
(e) If the rope suddenly breaks, calculate the initial acceleration
of the block down the slope. (2 marks)
Total for assignment: 62 marks