Cart Lab Report Preap Physics

Acceleration in Relation to Mass Amy Gong PREAP PHYSICS 10/26/2009

 Purpose: The purpose of this lab is to observe the two forces that work on and

against each other in a vector. The lab observes that principles of Newton’s second law of motion. Newton’s second law states that the acceleration of an object is directly proportional to the unbalanced force acting on it and indirectly proportional to its mass. The principle will be shown through the different masses that will be placed on a cart and hanging mass because as the hanging mass increases, the acceleration of the object being pulled should also increase.  Lab Set-up: There is a gray flat ramp placed on a level table that is .98 meters above the ground. Attached to the end of the ramp that in at the edge of the table is a round pulley and a stopper that will catch the cart. The cart is placed on the ramp and a black line is attached to the leading end of the cart, and the other end of the line is attached to a hanger that weighs 5g. The line is placed on the pulley to allow the weights that will be hung on the hanger to pull the cart forward towards the edge of the table. cart

pulley

ramp Table; .98 m high

weight

 Safety concerns: none  Procedure: First we set up a pulley, with a green cart attached on one end that

would run along a smooth surface and hanging weights on the other end that would pull the cart towards the edge of the table that is .98 meters above the ground. Next, we would add weights to the top of the cart and some to hanging end of the pulley. We would then run three trials timing how long it takes for the hanging weights to drop from the table edge to the ground. Then we would take some of the weights from the cart and add them to the hanging mass and repeat the previous step.  DATA: Mass Mass Time Distanc F net Accelerati Mass Mass Hung on of e pulled (N) on (m/s 2 ) of of (Kg) cart run (meter syste cart (Kg) (sec) ) m (Kg) (Kg) .055

.150

1.05

.98

.539

-1.78

.303

.153

.105

.100

.69

.98

1.029

-4.12

.250

.150

.205

0

.45

.98

2.009

-9.68

.207

.207

 CALCULATIONS: ➢ Fnet = (mass hung)*(Fgravity) (.055 Kg)(9.8 m/s2) = .539 Newtons ➢ Acceleration: Posf = Posi + Vit + .5at2 0 m = .98 m + (0 m/s)(1.05 s) + .5 (1.05)2a -1.96 = 1.1025a a = -1.78 m/s2 ➢ Mass of system = Fnet / acceleration .539 N / -1.78 m/s2 = .303 Kg ➢ Mass of cart = mass of system – mass on cart .303 Kg - .150 Kg = .153 Kg  Free Body Diagrams: 2) Framp Framp 1) .539 N

Cart & weights .303 KG

1.029 N

Fgravity

Cart & weights .250 KG

Fgravity

3) 2.009 N

Framp Cart .207 KG

Fgravity

 Conclusion & Questions:

➢ Why was the gravitational force of the hanging mass the net force of the system?  The gravitational force is the only force accounted for in the net force because there is no friction created that is pulling in the opposite direction. ➢ What are some weaknesses of the lab?  There are some data collection errors in the lab because with two different people starting the timer and releasing the cart, they do not act simultaneously. Also, the timer won’t be stopped at the same time the weights reach the ground because there is a reaction time from when it is perceived that the weight hits the ground to when the stop button is hit. Therefore, the time collected is off a little. ➢ How do these calculations account for the different calculations of the cart’s mass?  The reaction time for each trial will vary each time, so the timing error is different every time. Therefore, the accelerations will not be perfectly inverse to the mass that is hung and the mass of the system that is calculated will be more imprecise, leading to different mass of carts. ➢ Would it be more accurate to use a more massive hang weight or less massive hang weight to get a more accurate calculation of the cart’s mass? Why?

It would be more accurate to hang less weight because then the cart will accelerate at a lesser rate, and reaction time will be quicker, leaving less room for error. Using the free body diagram for the cart and the acceleration you calculated, find the tension in the string.  The tension in the string is equal to the force of the weights. 1) .539 N 2) 1.029 N 3) 2.009 N Why did we not need to know the tension in the string to calculate the cart’s mass?  The tension in the string remains constant throughout each run and it does not affect the cart’s mass. The lab effectively demonstrated Newton’s second law of motion because as the mass hung increase, the acceleration of the cart also increased proportionally. However, to attain more accurate results for the mass of the cart, the person who times the fall of the weight should stoop down directly in front of the weight so that he/she can perceive that the weight has hit the ground in a more accurate manner. 

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