Practice exam 1 PHYS1121_ Attempt review

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University of New South Wales *

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1121

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Physics

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Apr 3, 2024

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19/08/2021 Practice exam 1 PHYS1121: Attempt review https://moodle.telt.unsw.edu.au/mod/quiz/review.php?attempt=10071486&cmid=3806523 1/15 Dashboard  My courses  PHYS1121-PHYS1131-5216_00399  Quizzes  Practice exam 1 PHYS1121 Started on Wednesday, 18 August 2021, 3:33 PM State Finished Completed on Wednesday, 18 August 2021, 5:07 PM Time taken 1 hour 34 mins Marks 3.00/24.00 Grade 12.50 out of 100.00  Site Home  Announcements   User Guides School of Physics  COVID-19  Wellbeing & Health  Counselling PHYS1121-PHYS1131-PHYS1121-PHYS1131-Physics 1A-Higher Physics 1A - …  

19/08/2021 Practice exam 1 PHYS1121: Attempt review https://moodle.telt.unsw.edu.au/mod/quiz/review.php?attempt=10071486&cmid=3806523 2/15 Question 1 Partially correct Mark 2.00 out of 3.00 Question: A nerf gun is a toy that can shoot foam bullets. To use it, a bullet is loaded by pulling back on a spring. A button is then pressed that will release the foam bullet. The bullet has a mass of . When the nerf gun is fired horizontally from a height above the ground, the bullet lands on the ground horizontally from where it was fired. Assume that air resistance is negligible. Figure 1: A photo of a nerf gun and foam bullet. Part 1) How long does it take the bullet to reach the ground from when it leaves the nerf gun? 0.469 Your last answer was interpreted as follows: Part 2) What is the initial speed of the bullet as it leaves the nerf gun? 23.4 Your last answer was interpreted as follows: Part 3) What is the kinetic energy of the bullet as it leaves the nerf gun? 51.3 Your last answer was interpreted as follows: Your answer is partially correct. Feedback for Part 1) You have correctly answered this part. Feedback for Part 2) You have correctly answered this part. Feedback for Part 3) Kinetic energy is given by: .

19/08/2021 Practice exam 1 PHYS1121: Attempt review https://moodle.telt.unsw.edu.au/mod/quiz/review.php?attempt=10071486&cmid=3806523 3/15 Substitute into this equation, make sure you convert the mass of the bullet from to by dividing by 1000 when you substitute it in. Note: This answer should be correct to 3 significant figures. A correct answer is , which can be typed in as follows: 0.470 A correct answer is , which can be typed in as follows: 23.5 A correct answer is , which can be typed in as follows: 0.0516

19/08/2021 Practice exam 1 PHYS1121: Attempt review https://moodle.telt.unsw.edu.au/mod/quiz/review.php?attempt=10071486&cmid=3806523 4/15 Question 2 Incorrect Mark 0.00 out of 3.00 Question: A mass is pushed (a quick push is given to start it moving, in the question consider the motion after this push has stopped) down a long plane inclined at an angle of The initial speed of the block down the plane is down the plane, after it has traveled 1.00 m the speed has decreased to . Figure 1: Diagrammatic representation of a block of mass sliding down an inclined plane with initial velocity . The plane is inclined at degrees to the horizontal. Part 1) What is the acceleration of the block up the plane (i.e. positive answer if acceleration is up the plane, negative answer if it is down the plane). 3.79 up the plane Your last answer was interpreted as follows: Part 2) What is the net force on the block as it slides down the inclined plane? 21.6 up the plane Your last answer was interpreted as follows: Part 3) What is the coefficient of kinetic friction between the block and the plane? 0.386 Your last answer was interpreted as follows: Incorrect answer. Note: Your answers should be correct to 3 significant figures. Feedback for Part 1) Use the kinematic equation, . Take down the plane as negative and up the plane as positive. Use , and . Rearrange and solve for . Feedback for Part 2) Use Newton's second law: The acceleration was found in the first part and the mass of the block is . Feedback for Part 3)

19/08/2021 Practice exam 1 PHYS1121: Attempt review https://moodle.telt.unsw.edu.au/mod/quiz/review.php?attempt=10071486&cmid=3806523 5/15 The forces acting on the block parallel to the plane are the weight force (down the plane) and the frictional force (up the plane). Newton's second law tells us that the net force is the sum of these so: This can be re-arranged to give : Evaluate this. Feedback for Part 3) The forces acting on the block parallel to the plane are the weight force (down the plane) and the frictional force (up the plane). Newton's second law tells us that the net force is the sum of these so: This can be re-arranged to give : Evaluate this. A correct answer is , which can be typed in as follows: 2.36 A correct answer is , which can be typed in as follows: 4.84 A correct answer is , which can be typed in as follows: 0.644

19/08/2021 Practice exam 1 PHYS1121: Attempt review https://moodle.telt.unsw.edu.au/mod/quiz/review.php?attempt=10071486&cmid=3806523 6/15 Question 3 Incorrect Mark 0.00 out of 3.00 Question: Two masses and move towards each other on a frictionless track. has speed to the right while has a speed to the left ( Figure 1 ). They collide. The collision lasts s. After the collision moves to the right with a speed Figure 1: Diagrammatic representation of two masses, and moving towards each other on a frictionless track at speeds of to the right and to the left, respectively. Part 1) Before the collision what is the velocity of the centre of mass of the system? 0.28 Your last answer was interpreted as follows: Note: Give a negative answer if it is to the left. Part 2) What is the final velocity of 1.51 Your last answer was interpreted as follows: Note: Give a negative answer if it is to the left. Part 3) What is the average force on during the collision? 2.14 Your last answer was interpreted as follows: Note: Give a negative answer if it is to the left. Incorrect answer. Note: Your answers should be correct to 3 significant figures. Feedback for Part 1) The velocity of the centre of mass is given by: Substitute into this equation, except is negative as it is to the left. Feedback for Part 2) Momentum is conserved so: This can be rearranged to find In this case, is negative as it is to the left. Feedback for Part 3) The impulse is equal to the change in momentum so we can write:

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