DYNAMICS/KINEMATICS/CIRCULAR MOTION

Can someone please help with the following questions:

Q1:
the force to launch a rocket of a ship comprises of rocket thrust + force
from steam catapult. The rocket gives a force of 6 x 10^5 N force. Steam
catapult gives 4 x 10^5N force. The ship weighs 40 tonne and launch / ship
length is 75m long.
a)what is the kinetic energy of rocket as it leaves the catapult
b)the speed of the rocket as it leaves the catapult
c) the acceleration of the rocket
d) time it takes for operation

Q2:
A 3kg block + 2.5kg block slide together down a slope of 30degrees. The
coefficient of kinetic friction between block and slope is 0.51 for 3kg
block & 0.23 for 2.5kg block.
a)what is the acceleration of the pair

Q3:
A 20m diameter circular wheel shaped space station has all of its 5 x
10^5kg mass concentrated on the rim. The rotation rate of the mass at the
rim needs to have a radial acceleration equal to gravity. Rotation is done
by two rockets that give 100N tangential thrust. Rockets are on the rim of
space station.
a)how long will it take for space station to reach the required rotational
speed
b) how many revolutions will the station make in this time

Q4:
A tennis ball weighing 110g is stuck in a tree 8m from the ground. Standing
vertically below it, you throw a ball of mud weighing 250g at it. The ball
leaves your hand at 1.2m from the ground, and travels at 18m/sec. The mud
ball hits and sticks to the tennis ball. (Neglect interference from branch)
a) what's the maximum height reached by the tennis ball and mud ball
combination when stuck together.
b) the speed at which the combination hits the ground

Q5:
driving your car along at constant 15km/h you approach the traffic lights.
At the instant you hit the traffic lights, the lights change to green. You
then uniformly accelerate to 60km/h, which takes 12 seconds. You continue on
at constant 60km/h.
A second car waiting at the lights was stationary. You passed it at the
instant the lights changed green. The second car accelerates uniformly from
rest to 65km/h in 7 seconds, then maintains constant speed of 65km/h.
a) how long after the light changes green does the other car pass you
b) what speed are you doing when passed
c) what speed is the other doing when is passes you
d) how far from lights are you when passed


many thanks
polly

Dear Polly:

"polly" wrote in message
...

Can someone please help with the following questions:

Q1:
the force to launch a rocket of a ship comprises of rocket thrust + force
from steam catapult. The rocket gives a force of 6 x 10^5 N force. Steam
catapult gives 4 x 10^5N force. The ship weighs 40 tonne and launch /
ship
length is 75m long.
a)what is the kinetic energy of rocket as it leaves the catapult

change in KE is total force times distance.

b)the speed of the rocket as it leaves the catapult

v^2 = change in KE * 2 / mass

c) the acceleration of the rocket

acceleration = total force divided by mass

d) time it takes for operation

This is the only one requiring integration, and the formula is likely in
your textbook anyway.

Your go to school to learn how to learn. Not to learn how to get other
people to do your work for you (unless you are getting your MBA). Your
brain will be with you the rest of your life. Train it.

David A. Smith

"polly" wrote in message
...

Can someone please help with the following questions:

Q1:
the force to launch a rocket of a ship comprises of rocket thrust + force
from steam catapult. The rocket gives a force of 6 x 10^5 N force. Steam
catapult gives 4 x 10^5N force. The ship weighs 40 tonne and launch / ship
length is 75m long.
a)what is the kinetic energy of rocket as it leaves the catapult
b)the speed of the rocket as it leaves the catapult
c) the acceleration of the rocket
d) time it takes for operation

Q2:
A 3kg block + 2.5kg block slide together down a slope of 30degrees. The
coefficient of kinetic friction between block and slope is 0.51 for 3kg
block & 0.23 for 2.5kg block.
a)what is the acceleration of the pair

Q3:
A 20m diameter circular wheel shaped space station has all of its 5 x
10^5kg mass concentrated on the rim. The rotation rate of the mass at the
rim needs to have a radial acceleration equal to gravity. Rotation is done
by two rockets that give 100N tangential thrust. Rockets are on the rim of
space station.
a)how long will it take for space station to reach the required rotational
speed
b) how many revolutions will the station make in this time

Q4:
A tennis ball weighing 110g is stuck in a tree 8m from the ground.
Standing
vertically below it, you throw a ball of mud weighing 250g at it. The ball
leaves your hand at 1.2m from the ground, and travels at 18m/sec. The mud
ball hits and sticks to the tennis ball. (Neglect interference from
branch)
a) what's the maximum height reached by the tennis ball and mud ball
combination when stuck together.
b) the speed at which the combination hits the ground

Q5:
driving your car along at constant 15km/h you approach the traffic
lights.
At the instant you hit the traffic lights, the lights change to green. You
then uniformly accelerate to 60km/h, which takes 12 seconds. You continue
on
at constant 60km/h.
A second car waiting at the lights was stationary. You passed it at the
instant the lights changed green. The second car accelerates uniformly
from
rest to 65km/h in 7 seconds, then maintains constant speed of 65km/h.
a) how long after the light changes green does the other car pass you
b) what speed are you doing when passed
c) what speed is the other doing when is passes you
d) how far from lights are you when passed


many thanks
polly


This wouldn't be on your homework or take home test, now would it?

Instead of answering the questions, I'll tell you how I would get the
answers:

1. Start with a free body diagram of each object. That basically looks
like a square. On the first problem, there are two squares, one labelled
ship, the other plane. On the one marked "plane", put the forces that
affect the aircraft. Both the rocket thrust and the catapult push it in one
direction. If there were some other force pushing it up or whatever, you
would put that on too. The only force affecting the ship is the catapult,
which will push the ship backwards. If there were some sort of a rocket
blast shield, then some of the rocket thrust would affect the ship too.
We'll ignore that for now.

Ok. Total those forces up (remember which direction they are going).
Remember that old equation, f=ma ? Think that might be handy here? We have
the mass of each object (oh, yes, put the mass of the object inside the free
body diagram, just for bookkeeping). If we know f, and we know m, then
could we possibly know a? I'll bet with a little manipulation we could get
that.

Now, we find that the ship is 75 meters long. Remember that thing about
distance = 1/2at^2? Well, distance = 75meters, you found a just a moment
ago, and well, I'll guess that you can get t^2, then t from that.

Hmm, what do we have here. I see that we know the acceleration (in
meters/sec^2), and we know the time, and the initial velocity. Could we
possibly figure out the final velocity? From that, can you give the kinetic
energy?

Ok, your turn.

2. force body diagram again. This time put the masses sliding down a 30
degree slope. Gravity pulls them straight down, right? Unfortunately, the
slope is at 30 degrees, so we have to resolve those forces to be parallel
and perpendicular to the slope. A little trigonometry would help here,
wouldn't it. I guess it was the wrong class to sleep through. Oh, yes, the
problem..... I'll let you figure that out.
At any rate, the friction is going to act only on the force pushing
perpendicular to the slope. It will act as a force going uphill. The force
going downhill will try to pull the blocks downward, the force uphill
resists that. Add the two together (force is a vector, so adding gives a
smaller downhill force than without friction).

I've done enough physics for now. The same method works with the other
problems, more or less.

Michael