00:01
We have here distance r of t as a vector.
00:03
I want to work out v of t.
00:09
Just differentiate work out dr by dt.
00:16
To do that, just differentiate each component separately.
00:20
So the t here will become 1.
00:24
So simply i here, t squared here will become 2t, and t cubed 3t squared squared k.
00:37
That's my v vector.
00:42
Now i want to work out when t is two seconds, i want to find the speed.
00:52
So when t is 2, the vector, so v will be i plus 4j plus 12k.
01:05
Just replace t by 2 here and here.
01:12
That's v.
01:13
To work out speed, all i need do is find magnitude of that vector.
01:22
Square root of 1 squared plus 4 squared plus 12 squared.
01:30
Square root of 144 plus 16 plus 1 is the root of 161.
01:42
And that will be 12 .68, so 12 .7 to 3 .s...