Boston University IS480 Module 2 Assignment - Physics Problems

This document presents solutions to a physics assignment for Boston University's IS480 course, specifically focusing on Module 2: Newton's Laws of Motion. The assignment is divided into two parts: Part 1 includes the solution to several physics problems related to force, friction, acceleration, and free-body diagrams, drawing on concepts from Chapter 4 of the textbook. The solutions detail calculations for net force, acceleration, and gravitational force, along with explanations based on Newton's laws of motion. Part 2 describes a home experiment where the student investigates the effect of inclined plane height on the rolling velocity of a marble. The experiment involves measuring the time taken for a marble to roll down an inclined plane at different heights and analyzing the relationship between potential and kinetic energy. The document provides a detailed methodology, observations, and conclusions of the experiment, illustrating the principles of physics learned in the module.

Assignment 2.1
Question 1
Icy road has little frictional force. Frictional force is the force that opposes motion. For a car
to stop, the frictional force must be available to oppose the car motion for the car to stop.
During acceleration, the car needs the same force to have a grip on the road so as this
becomes possible.
Question 2
Given
Mass of the skater-50kg
Frictional force=-3N
Air resistance=-1N
The negative sign means the force is resisting the motion.
Required
a. Net force
Net force= Frictional force+ Air resistance =-3N+(-1N)=-4N
b. Acceleration
Equation relating force mass and acceleration is
Net force=Mass*Acceleration
Making acceleration the subject of the formula
Acceleration= Net force
mass =−4
50 =-0.08m/s2

Question 3
Given
Mass of car-1000kg
Pushing force-350N
Frictional force-125N
a. Free body diagram
b. Acceleration
c. Acceleration= Net force
mass =−4
50 =-0.08m/s2
Net force= 350-125=225N
Therefore, Acceleration= 225
1000=-0.225m/s2
Question 4
Given
Mass of rock-12kg
Acceleration-6.25m/s2
Required
Car
1000kg
125N
350N

a. Magnitude and direction of the net force
Net force= Mass*Acceleration
Therefore, force magnitude= 12*6.25=75N with the direction being downwards
b. Magnitude and direction of the gravitational force
Gravitational force is given as mass*gravitational constant
=12*9.81=117.72N with the direction being downwards
c. Magnitude of the air resistance
The air resistance can be calculated from an equation relating external force and drag.
Force=Weight-Drag
Therefore, Drag=Weight-Force
=117.72-75= 42.72N
Question 5
Given
Book mass-3kg
Box mass-7kg
Required
a. Weight
Weight=Mass*Gravitational constant.
=3*9.81=29.43N
b. Normal force the table exerts on the book

Force= (3+7)*9.81=98.1N
c. Normal force the book exerts on the box
Force =7*9.81=68.67N
Question 6.
From newton’s first law of motion, Clark fell backwards as the bus moved forward because
he was stationary and tended to remain in that position of rest while the bus he was in was
moving leading to inertia force acting on him thus he fell backwards.
Question 7
When Sarah is sitting on a chair, the two vertical forces acting on her are her weight which is
an action force on the chair and an equal and opposite reaction force from the chair. This
must be the case for her to remain sited. Action and the reaction forces must be equal and
opposite.
Assignment 2.2
Home experiment 3.
Topic: Rolling velocity of a marble
Objectives
To determine the effect of the height of the inclined plane on the marble roll velocity.
Method

Apparatus
i. Marble
ii. Ruler
iii. Smooth timber of different heights
iv. Timer
Procedure.
i. An inclined plane was made using the shortest timber and the height measured.
ii. The marble was held at the top of the inclined plane as shown in the figure above.
iii. The marble was released and the timer started simultaneously
iv. The timer was stopped immediately the marble hit the ground and the time taken
recorded.
v. This procedure was used for different timber sizes.
Measurements made.
The height of the inclined plane
Time taken for the marble to roll

Observation
The velocity of the marble increased with increase in the height of the inclined plane.
Discussion and conclusion.
The difference in the velocity of the marble for different inclined plane heights comes about
due to the difference in the potential energy possessed by the marble at different heights. The
potential energy is given by the formula Potential energy=Mass*gravity*height.
Since the gravity and the mass are constant, the height factor leads to the difference in the
potential energy. The potential energy increases with increase in the height of the plane as
indicated by the formula. The potential energy is usually converted into kinetic energy
causing the movement which is given as kinetic energy= 1
2 mass∗velocity∗velocity
This translates that the rolling velocity will increase with increase in kinetic energy due to
increase in potential energy as a result of increase in height.