How do you solve this maximum horizontal force physics problem?

Question

This is one question.. A sled weighing 60.0 N is pulled horizontally across snow so that the coefficient of kinetic friction between the sled and the snow is .100. A penguin weighing 70.0 N rides on the sled. If the coefficient of static friction between the penguin and the sled is .700, find the maximum horizontal force that can be exerted on the sled before the penguin begins to slide off.

Answer 1

If you accelerate the sled, you want the penguin to accelerate along with it. The coefficient of static friction says that the most horizontal force that can be transferred to the penguin is
Ff = (coefficient of static friction)*Normal force.
Since the snow is horizontal, the Normal force is its (his, her, kinda hard to tell) weight, 70 N. So
Ff = .100*70.0 = 7.00 Newtons

So the most the penguin can be accelerated is:
a = Ff/m = 7.00 N/(w/g) = 7.00 N/(70.0 N/9.8 m/s^2) = .98 m/s^2

The total mass is 130 N/g so the maximum horizontal force is
Fhmax = 130 N/g * .98 m/s^2 = 13 N.