Why does my hw say Your answer either contains an incorrect numerical multiplier or is missing one.?

Question

The position of a 2.75X10^5 N training helicopter under test is given by

r=(.020m/s^3)t^3i(i)+(2.2m/s)t(j)-(.060m/s^2)t^2(k)

Find the net force on the helicopter at t=5s

my answer: 6(0.020)5(i)-2(0.060)(k)

response:Your answer either contains an incorrect numerical multiplier or is missing one.?

Answer 1

Force is mass times acceleration.

Just looking at your first term (I can't read the last term for "r") you have calculated the acceleration by twice differentiating "r" , then evaluated it at t=5s. That's all fine for acceleration but now you have to multiply each term by the mass, (2.75/9.8)x10^5 kg

So, assuming both terms in your acceleration are correct, the force is then;

F = (2.75/9.8)x10^5x6x.02x5i - (2.75/9.8)x10^5x2x.06k

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat.

SHOW ANSWER