# Project #20645 - Physics

Question 1

This question is worth 30% of the total marks for this assignment and relates to the material in Chapter 1 and Chapter 3. As well as testing your understanding of Newton’s laws, forces and impulsive forces, it is designed to test your ability to clearly and concisely communicate physical principles to a reader.

A skydiver makes a controlled descent from an aeroplane to the ground. He undergoes a number of seconds of freefall at his terminal speed before opening his parachute, after which he decelerates to a new terminal speed. He continues to fall at this speed for some time before landing safely on the ground.

Describe the motion of the skydiver starting from the moment he leaves the aeroplane and finishing with him stationary on the ground. You should divide the descent into a number of phases. For each phase identify the vertical forces acting upon the skydiver, and describe his motion using Newton’s laws. Where it is useful to do so, as an approximation, you may treat the skydiver as behaving like a sphere during his descent.

You may include diagrams to make your answer clearer. These should be labelled and referred to in your account. Remember to define the frame of reference that you’re using to describe the motion. You may ignore any horizontal forces and motions, and your account should be about 600 words in length. Marks will be awarded for clarity and conciseness.

(30 marks)

Question 2

This question carries 17% of the marks for this assignmen.

A small toy (which is often found in party crackers) consists of a plastic or wooden figure attached to a spring and a suction device which will hold it to a smooth surface when the spring is compressed (see Figure 1).

Figure 1 For use with Question

When the toy is pressed down and made to stick to a glass table, the total compression of the spring is 1.2 cm. After a short time the vacuum seal fails and the toy pops up vertically into the air reaching a maximum height of 34 cm, then falls back down onto the table.

(a) Describe (in words and in a few sentences) the energy conversions that take place from start to finish during this process. (Ignore air resistance and all forces and energy associated with the operation of the suction device.) (6 marks)

(b) If the total mass of the toy is 0.65 g and assuming that the spring is ideal and that air resistance and other losses are negligible, calculate the spring constant of the spr ing. (Take g = 9.81 m s−2.) (5 marks)

(c) What is the magnitude of the force that has to be applied in order to compress the spring sufficiently so that the toy can be pressed down to the table? (3 marks)

(d) Calculate the speed with which the toy leaves the table. (3 marks)

Question 3

This question carries 23% of the total marks of this assignment.

(a)  A horizontal disc of diameter 12.0 cm is spinning freely about a vertical axis through its centre at an angular speed of 72 revolutions per minute. A piece of putty of mass 5.0 g drops on to and sticks to the disc at a distance of 4.0 cm from the centre. The angular speed reduces to 60 revolutions per minute. Calculate the moment of inertia of the disc. You should assume that no external torques are applied to the system during this process. (8 marks)

(b)  A constant tangential force is now applied to the rim of the disc which brings the disc to rest in 6.0 s. Calculate the magnitude of this forc e.      (8 marks)

(c)  Calculate the rotational energy of the system before and after the putty is added to the disc. Comment briefly on your answer. (7 marks)

Question 4

This question carries 30% of the total marks of this assignment.

Discuss and compare the principles of the Carnot cycle and the Brayton cycle as two different thermodynamic cycles.  You should give detailed descriptions of the processes that take place in each cycle and highlight the limitations of each and the differences between them. It is essential that you use fully labelled diagrams in your descriptions.

 Subject General Due By (Pacific Time) 01/09/2014 10:00 am
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