Physics --- Work and Energy --- Please help!!!!!!!!!!!!!!!!!!?

Question

1.At room temp., an oxygen molecule, with mass of 5.31 x 10^-26 kg, typically has a KE of about 6.21 x 10^-21 J. How fast is it moving?

2.An 80 g arrow is fired from a bow whose string exerts an average force of 95 N on the arrow over a distance of 80 cm. What's the speed of the arrow as it leaves the bow?

3.If the speed of a car is increased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver's reaction time.

4.A softball having a mass of .25 kg is pitched at 100 km/h. By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and pitcher is about 15 m.

5.A 220 kg load is lifted 21.0 m vertically with an acceleration a = 0.150 g by a single cable. Determine (a) tension in the cable, (b) the net work done on the load, (c) the work done by the cable on the load.

Please show work.

Equations:

W = m (v^2 / 2d)

KE = t/2 mv^2

W = 1/2 mv(2nd velocity)^2 - 1/2 mv(1 st velocity)^2

Answer 1

1. KE = (1/2)*m*v^2 - you have the KE and mass.

2. The amount of work done will be equal to the kinetic energy the arrow is given.
W = F*d = (1/2)*m*v^2 solve for v.

3. When the speed is increased 50% Vnew = 1.5*Vold. Kinetic energy will increase by 1.5^2 = 2.25.

Work done stopping it is Fbrakes*distance and equals the kinetic energy it has.
KEnew = 2.25*KEold so the stopping distance, SD, changes accordingly:
SDnew = 2.25*SDold

4. The acceleration on the baseball is given by
V^2 = Vo^2 + 2*a*d where V is final velocity, Vo is original velocity, a is acceleration, and d is distance. Finally,
F = m*a.

5.
(a) The tension is divided between holding the weight and accelerating it. T = W + m*a.
(b) The work gives the load a potential energy.
U = m*g*y
It also gives it kinetic energy. The velocity it has at the 21.0 m height is given by
V^2 = Vo^2 + 2*a*y. Use the velocity in the KE equation. The work done is the sum U + KE.
(c) Might be a trick, but this feels like semantics. I don't see that
b & c are any different. Maybe in class, or the book, some distinction was made between those 2 ways to say it?