Physical Science 101
Name _____________________
Partner’s Name ___________________
Equipment
cart, track, hanger and masses, photogate, card, cushion, pulley, meter stick, lab jack, string
Purpose Investigate work and energy relationships by doing two different experiments.
Show your work in the Data and Calculations space. Include all steps, labels and remember
Data
your units.
Definitions
Gravitational Potential Energy = mgh m
g
h
m
Kinetic Energy
v
mass
acceleration due to gravity
height above reference level
mass
speed
Total Mechanical Energy = KE+PE
x
y
Percent Difference
Part 1
second value
first value(most reliable value)
Gravitational Potential Energy
Purpose
In this experiment you will compare the gravitational potential energy stored in the hanging
mass to the kinetic energy that the system receives.
Procedure
1.
Set up the equipment as shown in Figure 1 on a level track.
Figure 1
2.
3.
Place 20 g (0.02kg) on the end of a string (mass + hanger). This is mhanger.
Determine cart’s mass. This is mcart.
Determine the system mass. Msystem = mcart + mhanger=________________
4.
Pull the cart back so that the hanging mass is approximately 0.30 to 0.50 m above the
5.
cushion. Measure the exact height to at least one decimal place. This is height h.
h=________________ m
Compute the initial potential energy of the hanging mass relative to the cushion.
6.
Remember : PE = mhanger g h
PE =_______________ J
7.
Let the mass drop and measure the final velocity of the system using a photogate timer.
Compute the final kinetic energy of the system, using Msystem. The cart should go through the
photogate just after the mass hits the cushion.
m = Msystem=____________ kg
x = cardlength=____________ m
t = time from photogate =___________ s
_________ m/s
=_____________ Joules
Calculate the percent difference between the initial potential energy of the mass
8.
(mhanger) and the final kinetic energy of the system (Msystem).
Is total mechanical energy conserved?
9.
Based on your data, would you say that energy was lost to friction? Explain
Part 2
Potential and Kinetic Energy
Purpose
In this experiment you will compare the gravitational potential energy stored in the cart to
the kinetic energy that the cart receives by changing heights.
Procedure
1.
Set up the equipment as shown in Figure 2, on a inclined track. Measure the height of the
cart above the table at positions 1 and 2. h1 = _______ h2 = ________
Figure 2
2.
Compute the potential energy of the cart at each of the two positions.
m= mcart = ____________________ kg
PE1=mgh1=________________ Joules
PE2=mgh2=________________ Joules
3.
Compute the CHANGE in potential energy between the two positions.
PE = PE1 - PE2 = ____________Joules
Place the cart at position 1 and release it from rest. Use the photogate timer to calculate the
4.
velocity of the cart at position 2. Remember : v = x / t, where x = length of the card and t = time
from the photogate and m= mcart .
_________ m/s
5.
=_____________ Joules
What is the kinetic energy of the cart at positions 1 and 2?
KE1=________________ Joules
KE2=________________ Joules
Calculate the TOTAL energy, E = KE + PE of the cart at positions 1 and 2.
6.
E1=________________ Joules
Is energy conserved? Explain.
E2=________________ Joules
Another important idea is the work energy theorem. It states that the work done by the net force
acting on an object equals the change in Kinetic Energy of the object.
Work = ? Kinetic Energy
Since Work is defined to be Force multiplied by the distance an object moves in the force’s direction,
the work energy theorem can be restated as,
Force x Distance = ? Kinetic Energy
Questions
1. How much work is done by an 80 N horizontal force which moves a cart 3.0 m?
2. What is the kinetic energy given to a car pushed by a 20.0 N force for a distance of 10.0 m?
3. What is the kinetic energy gained by a 20.0 kg rock just before hitting the ground if it falls from
a height of 2.0 m above the ground? Hint: what is its original potential energy relative to the
ground?
4. A rocket is projected vertically with 60 J of kinetic energy. As it goes up and comes back down
the air resistance force does -20 J of work on the rocket. What is the kinetic energy of the rocket just
before landing.