Physics 20/30 HELP PLEASEEE (work problems)?

Question

1)While lowering a 25 kg crate off the back of a 1m truck, a man exerts a force of 215N on the crate. How fast was the crate moving as it hit the ground?

2) A 55.2 kg box is pushed at a constant velocity up a frictionless ramp that is 10m long and 7m high. How much work will be done on the box in moving it to the top of the incline?
How much work will be done if the coefficient of friction is 0.18 between box and surface of the ramp?

8) An 18.8 kg object is accelerated from rest through a distance of 7.8m in 2.9s across a level floor. If the force due to friction between the object and the floor is 18.5N, what is the work done in moving the object?

9) A 12 255 kg truck traveling at 22.3 km/h is brought to a stop skidding 18m. Calculate work done by the truck by its brakes.
Calculate the work done by the trucks brakes if its initial speed was twice the vale stated above.




THANK YOU VERY MUCH!!

Answer 1

1)W-F=dF
dF=ma
a=dF/m
v=at
s=.5a’t^2
s=.5(g-a)t^2
t=sqrt(2s/(g-a)
Now since
v=(a) sqrt(2s/(g-a)
a==(W-F)/m)
a=(25.00 9.81 – 215)/25.0
a=1.21m/s^2
Finally
v=1.21 sqrt(2 x 1.0/(9.81-1.21))
v=0.58 m/s

2)
a)W=d w
W=h mg= 7m x 55.2kg x 9.81m/s^2
W=3791 Joules
b) Now W=h m g + f L +
f - is force of friction
L – total path = 10m
h – height = 7m
f=uN
N=force generated by weight normal to the surface
u – coefficient of friction
N=w cos(arcSin(h/L)
N=m g cos(arcSin(h/L)
f= u m g cos(arcSin(h/L)
f= 0.18 x 55.2 x 9.81 cos(arcSin(7/10))
f= 69.6 N
W=3791 + 69.6 x 10=4487 Joules

Oh my #8 and #9 you don’t expect me to all that, do you?