Simple work related physics questions?

Question

1. A block of mass 6 kg, which has an initial
speed of 2 m/s at time t = 0, slides on a
horizontal surface.
Calculate the work W that must be done
on the block to bring it to rest. Answer in
units of J.

2. If a constant friction force of magnitude
10 Newtons is exerted on the block by the
surface, find the acceleration of the block in
absolute value. Determine the speed v of the block as a function of the time t. Answer in units of m/s2.

Answer 1

1. The work to be done is equal to the kinetic energy
.5*m*v^2
12 J

2. F=m*a, so
10=6*a
a=10/6

since it is a frictional force
a=-10/6
so
v(t)=2-10*t/6

j