The displacement of an object attached to a spring and executing simple harmonic motion is given by x = 2×10-2 cosπt(in m). The time at which the maximum speed first occurs is?
A.
0.5s
B.
0.75s
C.
0.125s
D.
0.25s
Answer: Option A
Explanation:
Displacement, x = 2×10-2 cosπt Velocity, v = dx/dt=-2×10-2 πsinπt Velocity becomes maximum when Sinπt=1 πt=π/2 T=0.5s.
Natural length of spring is 60 cm and its spring constant is 4000 N/m. A mass of 20 kg is hung from it. The extension produced in the spring (take g=9.8m/s2) is?
A.
4.9cm
B.
0.49cm
C.
9.4cm
D.
0.94cm
Answer: Option A
Explanation:
In equilibrium, kx=mg x=mg/k=(20×9.8)/9000=0.049m=4.9cm.