KINEMATICS

Why Rockets have a fixed diameter?

Is it possible to create a rocket with a variable blast diameter to achieve different levels of torque and power similar to a geared transmission?

I suppose the best analogy I have is the difference in power between a garden hose normally and when you plug it with your thumb, creating more pressure.

Would it be possible to have a rocket launch with maximum diameter, and slowly close up like a camera shutter to gain speed once in the air? Perhaps this shudder would be angled like a funnel to direct the blast easier. All the rockets I see have a fixed diameter and it just makes me curious.

(Asked Bharath)

Experts in the field are requested to answer via comments

Momentum and Kinetic Energy

How it is possible to double the momentum of a body by increasing the kinetic energy four times?at the time what happen to mass?

Answer:

When we say, KE is increased, we mean to say by increasing speed alone unless otherwise specified.

Here mass remains constant.

Please note that the question says, KE of a body increased 4 times; which suggests that the body is the same and KE is increased by increasing the speed alone.

Solving problems from kinematics and friction

I just want to know how to easily solve problems related to kinematics and friction. I don’t know why i always face problem in these two topics a lot……
Please help and tell some tricks to solve these both…….
THANK U

Kinematics Problem

In a circus show a clown who is sitting on a post with height,H drops an apple to the ground.At the same time another clown throw an orange vertically upward from ground with speed 11 m/s.If both fruits pass each other after 0.8s, (a) determine the height (b) where do the apple and orange meet? (c) what is the speed of each fruit when they meet each other?

[Asked nur zainun syafiqah ayob]