Question

Billy pulls his Friend Sue on a sled at a constant velocity with the horizontal force of 200 N. The weight of the sled and Sue is 400 N. Which way will the sled move if Billy suddenly starts to pull with the force of 600 N?

Answer 1

Initially sled is moving with uniform velocity which means the net force must be balanced on the sled

$F_{applied} = F_{friction}$

So it is given that applied force on the sled is 200 N and sled is not accelerating so friction force must be 200 N.

$200 N = F_{friction}$

Now suddenly it starts with 600 N applied force due to which it will accelerate and this can calculated by Newton's II law

$F_{applied} - F_{friction} = ma$

$600 - 200 = \frac{400}{g} *a$

$400 = 40 * a$

$a = 10 m/s^2$

So in this case the sled ill start accelerating with acceleration $a = 10 m/s^2$