What is mantle convection?
a. cool matter rises and heats up and then falls and cools again and again, sometimes it will be erupted out of volcanoes
b. cool matter falls and heats up and rises and cools again and again, sometimes it will erupt out of volcanoes
c. cool matter rises and cools even more and then falls and heats up again and again, sometimes erupting from volcanoes

It's a snowy day and you're pulling a friend along a level road on a sled. you've both been taking physics, so she asks what you think the coefficient of friction between the sled and the snow is. you've been walking at a steady 1.5m/s, and the rope pulls up on the sled at a 32 ∘ angle. you estimate that the mass of the sled, with your friend on it, is 65 kg and that you're pulling with a force of 80 n .