Assignment 05 P115 2020 Solutions PDF

Preview

Summary

Download Assignment 05 P115 2020 Solutions PDF

Description

30 Sep 20

assignment-05-p115-2020-solutions.docx

PHYS 115 – Assignment 05 Solutions 1. - P115-A05-Q1-2020 [4824813] (a) An elevator of mass m moving upward has two forces acting on it: the upward force of tension in the cable and the downward force due to gravity. When the elevator is accelerating upward, which is greater, T or w? T

Both forces are equal.

w

(b) When the elevator is moving at a constant velocity upward, which is greater, T or w? T w Both forces are equal. (c) When the elevator is moving upward, but the acceleration is downward, which is greater, T or w? T w Both forces are equal. (d) Let the elevator have a mass of 1,375 kg and an upward acceleration of 2.9 m/s2. Find T. 17500 N Is your answer consistent with the answer to part (a)? Yes

No

(e) The elevator of part (d) now moves with constant upward velocity of 10 m/s. Find T. 13500 N Is your answer consistent with your answer to part (b)? Yes No (f) Having initially moved upward with a constant velocity, the elevator begins to accelerate downward at 1.50 m/s2. Find T. 11400 N Is your answer consistent with your answer to part (c)? Yes No

30 Sep 20

assignment-05-p115-2020-solutions.docx

2. - P115-A05-Q2-2020 [4824815] A crate with a mass of 3.00 kg starts from rest at the top of a 27.0° incline and slides 2.00 m down the incline in 1.45 s. (a) What is the magnitude of the acceleration of the crate (in m/s2)? 1.9 m/s2 (b) What is the frictional force (in N) acting on the crate? (Enter the magnitude.) 7.64 N (c) What is the coefficient of kinetic friction between the crate and the incline? 0.292 (d) What is the speed of the crate (in m/s) after it has slid 2.00 m? 2.76 m/s

30 Sep 20

assignment-05-p115-2020-solutions.docx

3. - P115-A05-Q3-2020 [4824816] As a mass tied to the end of a string swings from its highest point down to its lowest point, it is acted on by three forces: gravity (Fg), tension (T), and air resistance (R). (a) Which force does positive work? R T Fg (b) Which force does negative work? R T Fg (c) Which force does zero work? R

T

Fg

30 Sep 20

assignment-05-p115-2020-solutions.docx

4. - P115-A05-Q4-2020 [4824818] Three identical balls are thrown from the top of a building, all with the same initial speed. The first ball is thrown horizontally, the second at some angle above the horizontal, and the third at some angle below the horizontal, as in the figure below. Neglecting air resistance, rank the speeds of the balls and they reach the ground, from fastest to slowest.

1>2>3 2>1>3 All three balls strike the ground at the same speed. 3>1>2

30 Sep 20

assignment-05-p115-2020-solutions.docx

5. - P115-A05-Q5-2020 [4824821] A light spring obeys Hooke's Law. It takes 29.7 J of work to stretch this spring from an elongation of 4.15 cm to an elongation of 5.15 cm. (a) Is the amount of work required to increase the elongation of the spring from 5.15 cm to 6.15 cm greater than, less than, or equal to 29.7 J? greater than less than equal to (b) Verify your answer to part (a) by calculating the required work (in J). 36.1 J

30 Sep 20

assignment-05-p115-2020-solutions.docx

6. - P115-A05-Q6-2020 [4824822] A 7.80 g bullet is initially moving at 470 m/s just before it penetrates a block of solid rubber to a depth of 6.50 cm. (a) What is the magnitude of the average frictional force (in N) that is exerted on the bullet while it is moving through the block of solid rubber? Use work and energy considerations to obtain your answer. 13300 N (b) Assuming the frictional force is constant, how much time (in s) elapses between the moment the bullet enters the block of solid rubber and the moment it stops moving? 0.000277 s

30 Sep 20

assignment-05-p115-2020-solutions.docx

7. - P115-A05-Q7-2020 [4824823] Objects with masses m1 = 15.0 kg and m2 = 7.0 kg are connected by a light string that passes over a frictionless pulley as in the figure below. If, when the system starts from rest, m2 falls 1.00 m in 1.62 s, determine the coefficient of kinetic friction between m1 and the table. 0.353...