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please tell me your answer, all the step to the answer and why, i got the answer

ID: 1311385 • Letter: P

Question

please tell me your answer, all the step to the answer and why, i got the answer

Questions 9 and 10 refer to the following information: A spring is placed in a vertical position with its lower end supported by a horizontal surface. A stone of mass 4.0 kg is rested on the spring and compresses the spring by 0.02 m. QUESTION 9 The spring constant of the spring is closest to (a) 980 Nm (b) 1960 Nm (c) 0.784 Nm (d) 200 Nm QUESTION 10 The same spring is then placed horizontally and used to launch the stone along the smooth horizontal surface. The spring is compressed by 0.08 m by the stone and then the spring is suddenly released. The speed at which the stone leaves the spring is closest to (a) 1.8 ms (b) 2.5 ms (c) 6.3 ms (d) 3.1 ms

Explanation / Answer

9)
By conservation of energy
potential energy of mass = compression energy of spring
mgh = 0.5*K*x^2
here m = 4 , h = 0.02 m , x = 0.02 m
so, 4*9.8*0.02 = K*(0.02)^2
k=1960 Nm-1 is the answer

10)
the energy stored in spring = 0.5*K*x^2 = 0.5*1960 *(0.08)^2 = 6.272 J
if all this is converted into kinetic energy
6.272 = 0.5*m*V^2
6.272 = 0.5* 4*V^2
V = 1.8 m/s is the answer