Newton's second law:
We're told that the video is recorded at 60 frames per second.
This means that 1 frame = 1/60 seconds.
6 frames would be, 1/10 s
Video text description for the Direct Measurement Video of Newton's Second Law - Fan Cart
In this video, a small cart that has a mass of 600 grams rests on a table top. There is a fan on top of the cart, blowing air backwards at a steady rate. A stretched spring is attached to the back of the cart by a string, holding it in place. A scale, marked off in newtons, is positioned next to the spring and a small dot at the end of the spring indicates the magnitude of the spring force. The spring and scale together is called a "dynamometer." Before the cart is released from the spring, the dynamometer reads approximately 1.9 newtons. The video is recorded at 60 frames per second, resulting in playback motion 2 times slower than normal. A frame counter indicates the current frame. A horizontal distance scale, marked off in centimeters, is also shown on the video. While the cart is at rest, the front edge of the front wheel is at the zero of the scale.
At frame 245, the string that attaches the cart to the spring is cut, releasing the cart, and it begins to roll forward. Using the distance scale, the position of the front edge of the front wheel can be tracked with time. The following table indicates the position at different frames.
A. What is the magnitude of the thrust force before the cart is released? Express your answer in newtons using three significant figures.
B. According to Newton's second law, what is the acceleration of the released cart? Use 1.9 N as the magnitude of the thrust force. Remember that you may assume that the thrust force remains constant throughout the experiment. Also, neglect the resistive forces everywhere. Express your answer in meters per second squared using three significant figures.
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