Hooke's law describes a certain light spring of unstretched length 38.0 cm. When one end is attached to the top of a door frame and a 8.00-kg object is hung from the other end, the length of the spring is 41.0 cm.(a) Find its spring constant. kN/m(b) The load and the spring are taken down. Two people pull in opposite directions on the ends of the spring, each with a force of 170 N. Find the length of the spring in this situation. cm
Question
Hooke's law describes a certain light spring of unstretched length 38.0 cm. When one end is attached to the top of a door frame and a 8.00-kg object is hung from the other end, the length of the spring is 41.0 cm.(a) Find its spring constant. kN/m(b) The load and the spring are taken down. Two people pull in opposite directions on the ends of the spring, each with a force of 170 N. Find the length of the spring in this situation. cm
Solution
(a) To find the spring constant (k), we can use Hooke's Law, which states that the force exerted by a spring is equal to the displacement from the equilibrium position multiplied by the spring constant. The formula is F = kx.
First, we need to find the displacement (x). The spring was initially 38.0 cm long and stretched to 41.0 cm, so the displacement is 41.0 cm - 38.0 cm = 3.0 cm. We need to convert this to meters, so x = 3.0 cm * (1 m/100 cm) = 0.03 m.
The force (F) exerted on the spring is equal to the weight of the 8.00-kg object, which is mass times gravity. So, F = m*g = 8.00 kg * 9.8 m/s^2 = 78.4 N.
Now we can find the spring constant using the formula k = F/x = 78.4 N / 0.03 m = 2613.33 N/m or 2.613 kN/m.
(b) When two people pull the spring with a force of 170 N each, the total force on the spring is 2*170 N = 340 N.
We can find the new displacement of the spring using the formula x = F/k. Substituting the values we have, x = 340 N / 2613.33 N/m = 0.13 m.
To find the new length of the spring, we add this displacement to the original length of the spring. The original length was 38.0 cm, which is 0.38 m. So, the new length is 0.38 m + 0.13 m = 0.51 m or 51.0 cm.
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