Hanging Mass and Car
How do the predicted velocity and the measured velocity compare in each case? Did your measurements agree with your initial prediction? If not, why?
Our experimental measurements did not agree with out initial predictions as our calculated values for all experiments were slightly larger than the values we gathered from our experiment. There could be a few possible reasons our experimental values did not match up with our calculated values, and those are the friction in the pulley or track, air resistance, stretching or slippage of the string, and human error measurements. In our calculated values we assumed the system had an ideal pulley and we did not account for friction nor air drag in our calculations.
Does the launch velocity of the car depend on its mass? The mass of the block? The distance the block falls? Is there a choice of distance and block mass for which the mass of the car does not make much difference to its launch velocity?
Yes, the launch velocity of the car depends on all three factors (the mass of the car, the mass of the block, and the distance the block falls). A heavier block will increase velocity, a heavier car will decrease velocity, and a greater distance that the block falls will increase the velocity as well.
If the same mass block falls through the same distance, but you change the mass of the cart, does the force that the string exerts on the cart change? In other words, is the force of the string on object A always equal to the weight of object A? Is it ever equal to the weight of object A? Explain your reasoning.
Yes, the force of that the string exerts on the car does not change if the mass of the car changes. The force on the car is the tension in the string, and this tension is not always equal to the weight of the block. The tension is only equal to the weight of the block if the block is in free fall (i.e., if the car is massless or if there is no opposing force). The tension of the rope will increase with the mass since it is accelerating a heavier car.
Was the frictional force the same whether or not the string exerted a force on it? Does this agree with your initial prediction? If not, why?
No, the frictional force was not the same when the string was pulling the car and after the string stopped exerting a force. When the string is pulling the car the frictional force opposes the motion as the car is being accelerated by the tension in the spring. After the string stops pulling the car the car will continue moving due to its momentum, and the friction is the only force acting on it to slow it down. The frictional force remains the same in magnitude, but now it is the only force acting to slow the car.
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