00:01
Hi, in this question given that mass equals 10 kg and f equals 170 cos 8t and l equals 9 .8 cm.
00:21
So, l can be written as 9 .8 into 10 power minus 2 meter.
00:27
In part a, we need to determine the spring constant k.
00:33
We know that the formula f equals k into l.
00:37
F can be written as mg equals kl.
00:41
On substituting all the known values, then we get k equals mg by l which is equal to 10 into 9 .8 divided by 9 .8 into 10 power minus 2 which is equal to 1000.
00:57
Hence, let's conclude that for part a, answer k equals 1000 n per meter.
01:04
Next, move on to part b.
01:08
Here, we need to formulate the initial value problem y of t.
01:12
So, here f equals 170 cos 8t.
01:18
Therefore, we can write it as m d square y by dt square plus c dy by dt plus ky equals f of t.
01:31
On substituting all the known values in this, then we get 10 y double dash plus 0 plus 1000 y equals 170 cos 8t which implies 10 into y double dash plus 100 y equals 170 cos 8t.
01:57
So, we can further simplify y double dash plus 100 y equals 70 cos 8t.
02:06
Here, 0 and 0 cancel each other.
02:09
So, next we need to write the complementary solution.
02:13
For that purpose, first we need to write the axillary equation which is r square plus 100 equals 0.
02:22
Therefore, r equals plus or minus 10i...