Download Lab #4: Big Truck

Lab: Big Truck
Conceptual Physics
Objective: To verify Newton’s Second Law of Motion. Determine how net force and mass
affect the acceleration of an object.
Assumptions:
 Mass of truck and driver is 1600 kg.
 Each student in the truck has a mass of 60 kg.
 Each pusher pushes with equal force, and with a constant force for the entire distance.
Materials: Large vehicle, meter sticks, stopwatches, students
Procedure:
Part 1:
Students will time how long it takes to push a truck from rest, for a distance of five meters.
Four trials will be run as outlined below.
 Trial 1: 1 students pushes a fully loaded truck (9 students in the vehicle)
 Trial 2: 3 student pushes a fully loaded truck (9 students in the vehicle)
 Trial 3: 1 students pushes an empty truck (no students in the vehicle)
 Trial 4: 3 student pushes an empty truck (no students in the vehicle)
Student tasks: 4 pushers, 9 students as passengers, 2 timers (one timer is also a coordinator)
Part 2:
Record the time in the data table. In the space provided below, record the trial for which you
will do calculations. Use kinematics to solve for the acceleration and use Newton’s Second
Law to calculate the Fnet for one trial. Round your Fnet to the nearest 10 N.
Trial
vi = 0 m/s
d=5m
t=
Data Table:
# of
pushers
1
# of
students in
truck
9
3
Time (s)
Distance
(m)
Acceleration
(m/s2)
Mass (kg)
5
2140
9
5
2140
1
0
5
1600
3
0
5
1600
Fnet (N)
Analysis and Discussion Questions:
1. In the space below, draw a free body diagram of the truck being pushed from rest. Include
velocity and acceleration arrows. Include and label all forces acting on the truck. Represent the
unbalanced force with the longest arrow.
2. If you add up the Fnet in the data table, that represents the total force for eight students. Use
the information in the data table to calculate the approximate net force exerted by a typical
student. (Show work.)
3. How does increasing the net force affect the acceleration? Use information in the data and
compare trials to support your answer. (You must determine which trials to compare.)
4. What would happen to the acceleration of a full truck if six students pushed the truck?
Compare your prediction to one of the trials performed in the lab.
5. How does increasing the mass affect the acceleration? Use information in the data and
compare trials to support your answer. (You must determine which trials to compare.)
6. In an ideal world, with no friction in the axle, what would happen if a first-grader pushed the
fully loaded truck? Draw a free body diagram of the truck to show this situation.