help on physics homework?

we will use both kinematic equations and newton's laws in this question

first, we use the information about the 3.2 kg mass to determine its acceleration

using vf^2=v0^2+2ad

where vf=final speed = 1.28 m/s

v0=initial speed = 0

a=acceleration (to be calculated)

d=distance = 0.399m

we have

1.28^2=0+2a(0.399) or a=1.28^2/2(0.399) = 2.05m/s/s

now, write newton's second law for the two masses:

sum of forces = ma

for the block on the table, the forces are tension and friction, so we have

T-f=ma where m=4.85kg and a=2.05m/s/s since the string has the same acceleration throughout

for the hanging block, we have

T-mg = -ma (note the minus sign on the right, this is because the block is accelerating downward, and we have already defined T as the positive direction)

T-3.2g=-3.2(2.05)

our two equations are:

T-f=4.85(2.05)N = 9.9N

T-3.2g=-3.2(2.05)N=-6.6N

subtract equations:

-f + 3.2 g = 16.5N

f = 3.2g-16.5N = 3.2x9.8N-16.5N=14.9N

and this is the frictional force acting on the 4.85 kg block