Physics Help!!!!?

Question

1. An object of mass 2.6 kg that is initially at rest is accelerated by a constant force.  After the force acts on the object over a distance of 2.1 m, the speed of the object is 5.5 m/s.  What is the magnitude of the force in newtons?  

2. A block slides on a horizontal surface with an initial speed of 22 m/s.   If the block takes 4  s to come to a stop, what is the coefficient of kinetic friction, μk between the block and the surface?  Take g = 10 m/s2. 

Answer 1

first find the acceleration

v² = v₀² + 2ad

5.5² = 0² + 2a(2.1)

a = 30.25/4.2 = 7.20 m/s²

now use F = ma

F = 2.6•7.2 = 20.2 N

2) first find the acceleration

a = Δv/Δt = 22/4 = 5.5 m/s²

F = ma = 5.5m N

weight of block w = mg = 10m

μk = F/w = 5.5m/10m = 0.55