Physics Assignment: Frictional Force, Net Force, and Rolling Velocity

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
1000k
g
Car
350N 125N

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