Physics Coursera Tests WEEK 4 PDF

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This is my coursework for this subject i hope it helps for references and notes...

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PHYSICS COURSERA TESTS WEEK 4 WEEK 4 PRACTICE QUIZ: NEWTON'S LAWS OF MOTION 1. A bicycle is travelling at constant velocity on a horizontal road. Select all of the following statements that are true: ANS: Various forces are acting on the bicycle, and their sum is zero 2. TRUE or FALSE: The 'natural state' of matter is zero velocity. ANS: False 3. Aristotle was stupid. ANS: False

4. From the following list, choose ALL statements that are true. Think carefully, because this question needs thought. (Also, as an exercise, think of counter-examples for the ones that are false.) ANS:zero total force implies zero acceleration zero velocity implies zero speed zero speed implies zero velocity

5. Friction always slows things down. ANS: False

6. Venus travels at approximately constant speed around the sun because ANS: there is almost no force acting on it in the direction of its velocity.

PHYSICS COURSERA TESTS WEEK 4 WEEK 4 PRACTICE QUIZ: INERTIAL AND NON-INERTIAL FRAMES 1. What is your weight? Give your answer in newtons. (Don't use exponent notation) My weight = ______ N. ANS: 260

2. An elephant has a mass of 3200 kg. What is the elephant's weight? Give your answer in kN (and remember significant figures). Elephant's weight = ______ kN. ANS: 31

3. Consider the equation \boldsymbol Ftotal = ma. This equation is: ANS: : effectively a definition of force a definition of (inertial) mass a law of science and therefore, in principle, something that can be disproved 4. A ball with mass 230 g is travelling horizontally to the right at 5.0 m⋅s−1. It rebounds against a wall and moves to the left, also horizontally, with an initial speed of 3.8 m⋅s−1. It is in contact with the wall for 39 ms. (Neglect any vertical motion.) Taking right as the positive direction, what is the average force exerted by the wall on the ball during the collision? Average force exerted = ______ N to the right. (use the correct number of sig figs!) ANS: -52

5. A car has a mass of 1100 kg. What average force is required to accelerate it to 21 m/s in 11 s in a straight line? Give your answer in kN. Magnitude of the required force = ______ kN. (use correct number of sig figs) ANS: 2.1

6. Joe's weight, to two significant figures, is 700 newtons down. What is the magnitude of the total force he needs to apply in order to accelerate at 2.0 m.s−2? Magnitude of required

force to accelerate Joe = _____ N. ANS: 140

PHYSICS COURSERA TESTS WEEK 4

7. An object travels in a circle at constant speed. Select all the TRUE statements: ANS: The angle between v ∧a is 90° .

PHYSICS COURSERA TESTS WEEK 4 WEEK 4 PRACTICE QUIZ: NEWTON'S THIRD LAW 1. A ball falls vertically, hits the ground and then rises vertically. The weight of the ball is W. During the collision, the ball exerts a downward force Fb on the ground and the ground exerts an upwards force Fg on the ball. Throughout the collision, which of the following is true: ANS: 2. I'm standing (barefoot) on the floor and, as usual, my weight W acts downward. Which other force makes the Newton pair for W? (If you really insist, if W is the action force, what is the reaction force?) If necessary, scroll down to see all options. ANS: The gravitational attraction that my body exerts on planet Earth 3. The mass of the earth is about 80 times greater than that of the moon. Identify all of the following that is/are true (ignore all effects except the earth-moon interaction): ANS: Due to the forces they exert on each other, the magnitude of the earth's acceleration towards the moon is about 80 times smaller than that of the moon's acceleration towards the earth 4. Big Barry has a mass of 100 kg. Slim Sal has a mass of 50 kg. They stand, facing each other, on their skateboards, whose masses are negligible and which roll without friction. Then Sal pushes against Barry. This question concerns their accelerations during the push. Be careful, and remember that accelerations are vectors. (One significant figure will do.)

ANS: -2 5. Same as the previous question: Big Barry has a mass of 100 kg. Slim Sal has a mass of 50 kg. They stand, facing each other, on their skateboards. The difference is that this time Barry pushes Sal. But we ask the same question concerning their accelerations?

ANS: -2 6. Peter's mass is 85 kg. He stands on bathroom scales, whose mass is 2.0 kg. What force do the scales exert on (i) Peter and (ii) the floor? Take the positive direction as up. The scales exert _____ N upwards on Peter, and ______ N upwards on the floor. (Separate your answers by a comma, think about the sign of your answers, and don't forget your significant figures.). ANS: 830, -850

PHYSICS COURSERA TESTS WEEK 4 WEEK 4 PRACTICE QUIZ: CALCULATING TOTAL FORCE

1. Jill stands on a skateboard, whose light wheels roll without friction. The combined mass of Jill and the skateboard is 55 kg. She is holding one end of a light, inextensible rope, which is horizontal, and she is pulling on it with a force of 120 N. On the other end, Jack, standing stationary on the ground, is pulling on the rope with force of 120 N. What is the magnitude of Jill's acceleration? (Remember significant figures.) Magnitude of Jill's acceleration = _____ m⋅s−2. ANS: 2.2

2. A light, inextensible string passes over a light pulley that turns without friction. One end of the string is attached to a mass mm. The other is attached to a mass M=2m. The string has a tension T. We want to analyse the motion of this system. However, we'll do it in easy steps.

Let a be the upwards acceleration of mm. Which of the following is true? ANS: a is greater than 0. (i.e. mm is accelerating upwards) 3. Refer to the pulley system described above. Let a be the upwards acceleration of mm. What is the upwards acceleration of M? ANS: -a 4. Refer to the pulley system described above (it is light and turns without friction). Which of the following is true about the tension in the string supporting M? ANS: The tension in the string supporting M is approximately equal to the tension in the string supporting m. 5. Let a be the upwards acceleration of mm and T be the tension in the string. Which of the following gives the correct expressions for Newton's 2nd law applied to masses m and M:

ANS:

PHYSICS COURSERA TESTS WEEK 4 6. We how have:

Using these results from part D, find a very simple expression for the acceleration aa in terms of g. Acceleration = _______. ANS: 7. An easy one: The dimensions and base units for force are (fill in the exponents): Force = massa ∙ lengthb ∙ time c Write your answer as a, b, c ANS: 1, 1, -2

8. A more difficult one – that we noticed in Week 3. When can we neglect air resistance in comparison with other forces? Let's find out. Air resistance is the force required to move air out of the way*, which requires accelerating it. The acceleration of the air depends on how fast the object is travelling (speed |v|). The mass of air accelerated depends on the density of the air (\rhoρ), the cross sectional area A of the object and also on how streamlined the object is. So let's guess at the formula and write

where N is a pure number that is different for different shapes (e.g. smaller for streamlined objects). Using the method of dimensions, find the values of a, b and c. Important: you could look up the formula for air resistance but (i) that means that you wouldn’t learn a really cool technique and (ii) that would be cheating. (And cheating when there are no marks involved would be pretty weird!) So, instead, here are some hints:

* Imagine a large flat plate moving in the normal direction: some air in front of it is accelerated up to the speed of the plate. We'll come back to this problem after we've done work and energy in week 6. Strictly, we could also include the viscosity of the air, but this is only important for very small objects. For water (or honey!), viscosity is not so often negligible.

ANS: 1, 1, 2...