You are sitting in a chair and you are ready to kick a soccer ball from a sitting position using only your quadriceps muscles to rotate your knee. Be sure you will not pivot your hips, as you are sitting in the chair; we want to simplify this problem to include only rotating your lower leg at the knee joint and keeping your thigh firmly fixed to the seat. For our purposes, your quadriceps muscles can be treated as a single string that exerts a tension on the knee at a right angle from a lever arm of 2.00 cm. The knee is connected to a plausible 50.0 cm lower leg as measured from the pivot point of the knee to the contact point where we will kick the ball. Before we kick it, we would like to balance the ball on our contact point (at our ankle, say) 50.0 cm away from the pivot point of the knee by extending the lower leg straight out (upper leg aligned with the lower leg). The soccer ball has a mass of 400 grams. We will neglect all mass of all parts of the leg here for brevity c) We now wish to kick the ball from rest on the floor to a speed of 14.0 m/s. If we maintain contact with the soccer ball for 0.0100 seconds, what tension force should the idealized quadriceps muscles exert on the knee joint in order to achieve this soccer ball speed? d) A 14.0 m/s soccer ball kick is plausible for the average person. Do you think the human body is an amazing machine by looking at the tension generated by the quadriceps muscles during the contact time of the soccer ball kick?
You are sitting in a chair and you are ready to kick a soccer ball from a sitting position using only your quadriceps muscles to rotate your knee. Be sure you will not pivot your hips, as you are sitting in the chair; we want to simplify this problem to include only rotating your lower leg at the knee joint and keeping your thigh firmly fixed to the seat. For our purposes, your quadriceps muscles can be treated as a single string that exerts a tension on the knee at a right angle from a lever arm of 2.00 cm. The knee is connected to a plausible 50.0 cm lower leg as measured from the pivot point of the knee to the contact point where we will kick the ball.
Before we kick it, we would like to balance the ball on our contact point (at our ankle, say) 50.0 cm away from the pivot point of the knee by extending the lower leg straight out (upper leg aligned with the lower leg). The soccer ball has a mass of 400 grams. We will neglect all mass of all parts of the leg here for brevity
c) We now wish to kick the ball from rest on the floor to a speed of 14.0 m/s. If we maintain contact with the soccer ball for 0.0100 seconds, what tension force should the idealized quadriceps muscles exert on the knee joint in order to achieve this soccer ball speed?
d) A 14.0 m/s soccer ball kick is plausible for the average person. Do you think the human body is an amazing machine by looking at the tension generated by the quadriceps muscles during the contact time of the soccer ball kick?
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