physics help?

Question

A box of books weighing 319 N is shoved across the floor by a force of 48s N exerted downward at an angle of 35 degrees belown the horizontal.
a) ifthe coefficient of kinetic friction between teh box and the floor is 0.57, how long does it take to move the box 4 m, starting from rest
b) if coefficient of kinetic friction between the box and the floor is 0.75, how long does it take to move the box 4 m, starting from rest?

A 3 kg block starts from rest a the top of a 30 degree incline and accelerates uniformly down the incline, moving 2 m in 1.5 s
a) Find the magniutde of the acceleration of the block
b) find th coefficient of kinetic frction between the block and the incline.
c)Find the magnitude of the frictional force acting on the block
d) find the speed of the block after it ha slid a distance of 2 m

Answer 1

1a. Use the following formulae:
F=Ma
s=ut+1/2at^

Horizontal component of force 35 degrees below horizontal = 48cos35N (You wrote 48sN. I disregarded the s)

kinetic force of friction, f=uR, where u is the coefficient
and R is the force normal to the surface.
u=0.57
R=319+vertical component of downward force
= 319+48sin35
f=0.57*(319+48*0.574)
=197.6N
Net force F=f-48cos35
=197.6-48*0.819
=158.3N
Substitute known values in F=Ma:
158.3=319/9.8*a
a=158.3*9.8/319
=4.86m/s^2

Substitute known values in s=ut+1/2at^2
4=0*t+1/2(4.86)t^2
t^2=4*2/4.86
=1.64
t=0.41s

You can do 1b now, right?
2a. Use the formula s=ut+1/2at^2 again. All values are
given except a. You can do that now, I'm sure.
2b. Use the formula f=uR. Just follow the example in 1a. above.
2c. and 2d. These are for you to do also.

Good luck. You might sweat a little doing all these, but when it comes to exam time, you will be rewarded. From my experience, a person does better in an exam, if he does the exercises himself. That is, after some pointers from others..like the ones I'm giving you here.