2. A student is pulling a 11.0 kg sled along flat ground. The students 30.0 kg sister then sits in the sled. The student then applies a 430 N force at an angle of 35° N of E. If the force of friction is 180 N, what is the acceleration of the sister sitting in the sled. (Ensure you draw a free body diagram.) ​

Explanation:

The equation for this is

F - f = ma

The thing that gets strange here is that, because the student is pulling his sister on the sled with the rope at an angle, some of his efforts are being wasted. The sled is only going to move forward (horizontally), so the vertical component of that force is useless. He's not actually pulling horizontally with that much force; we have to figure out how much using the following equation:

to get that

F = 352 N

Everything else falls into place quite easily into the equation now:

352 - 180 = 41a and

172 = 41a so

a = 4.2 m/s/s

measuring things 1 litre of water