PHYSICS-1
WORK AND ENERGY
EXPERIMENT-7 Work and Energy
OBJECTIVE
The purpose of this experiment is to apply the concept of the work and energy to calculate the
work done by the force of friction between a car and a wooden board as they slide relative to
each other at constant velocity. We study it for the case of the car moving up and down the
incline.
MATERIALS
Wooden Board
Weight hanger
Protractor
Car
Balance
Slotted weights
Pulley
INTRODUCTION
In general, friction is the force that slows down the motion of an object. The force of friction is
directed along the surface of contact between the object and surface and directed opposite
to the direction of motion of object.
Car moving up:
For the car of mass M moving up the incline at constant
speed, we can show, from 2nd law of motion, that the force
of friction f is given by:
f = ρ g – M g sinθ
(1)
where ρ is the mass hanging from the other side of the
pulley which makes the car move up.
Car moving down:
Now, for the car of mass M moving down the incline at constant speed, we can show, from 2 nd
law of motion, that the force of friction f is given by:
f = M g sinθ – η g
(2)
where η is the mass hanging from the other side of the pulley which makes the car move down.
And finally the work done by friction becomes:
Wf = f d
(3)
Where d is the distance the car travels along the board.
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PHYSICS-1
WORK AND ENERGY
EXPERIMENTAL PROCEDURE
1)
Determine the mass M of the car and record it.
2)
Set up the board and the car as shown in figure 1 with an incline angle of 300 with the
table. Position the car near the bottom of the incline and record its initial (vertical) height
h1. Add enough weights of mass ρ on the weight hanger to make the car move up the
incline at a very slow speed after given a slight tap. Record the initial height H1 of this
weight. Measure also the distance d that the car travels along the board.
3)
When the car reaches near the top of the incline, record now its height h2 and that of the
weight hanger H2. Start removing weights from the weight hanger until the car starts
moving down the incline at a slow speed after given a small tap. Record this mass η.
4)
Repeat the above procedures for an incline angle of 600.
CALCULATIONS
1) Compute the frictional force f and the work W f done by friction for the incline angle
of 300, while car is going up, and down. Record in the table on page 3.
2) Compute the frictional force f and the work Wf done by friction for the incline angle
of 600, while car is going up and down. Record in the table on page 3.
3) For each angle, compute the percent difference in the two values of the work W f.
Record in the table on page 3.
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PHYSICS-1
WORK AND ENERGY
EXPERIMENT 7 – Work and Energy
REPORT FORM
Part 1
Name: __________________________________
Car moving up the incline
Mass M of car ____________
Angle of
incline
Mass
ρ
(g)
Distance
travelled
by car
d
(cm)
Initial
height
of car
h1
(cm)
Final
height
of car
h2
(cm)
Initial height
of suspended
mass
H1
(cm)
Final height
of
suspended
mass
H2
(cm)
f
(from
eqn 1)
Wf
(from
eqn 3)
(N)
(J)
f
(from
eqn 2)
Wf
(from
eqn 3)
(N)
(J)
300
600
Part 2
Angle of
incline
Car moving down the incline
Mass
η
(g)
Distance
travelled
by car
d
(cm)
Initial
height
of car
h1
(cm)
Final
height
of car
h2
(cm)
300
600
Percent difference in Wf for θ = 300 _________
Percent difference in Wf for θ = 600 _________
3
Initial height
of
suspended
mass
H1
(cm)
Final height
of
suspended
mass
H2
(cm)
PHYSICS-1
WORK AND ENERGY
EXPERIMENT -7: Work and Energy
Post- laboratory Questions
Name: ______________________________________
1) Compute the percent energy lost to friction for the car moving up the incline for both
angles.
2) For θ = 600, compute the work done by each force acting on the car. Should they add up to
zero? Explain.
3) For θ = 300, compute the normal force acting on each wheel of the car?
4) Is friction in this experiment only due to the car? Explain.
5) Show that, for the car moving up the incline, that the coefficient µ of friction is given by:
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