Please help me with energy?

Question

I really need help in this subject. Everyone says it is easy...but I just don't understand it. I have a few questions that I feel cover the areas where I am lost. Please explain the questions and how to find the answers. Also if you would like, please solve them.

1. A compact car and a trailer truck are both traveling at the same velocity. Did the car engine or the truck engine do more work in accelerating its wehicle?

2. A 10.0-kg test rocket is fired vertically from Cape Canaveral. Its feul gives it a kinetic energy of 1960 J by the time the rocket engine burns all of the feul. What additional height will the rocket rise?

3. Pam, wearing a rocket pack, stands on frictionless ice. She has a mass of 45 kg. The rocket supplies a constant force for 22.0 m, and Pam acquires a speed of 62.0 m/s. What is the magnitude of the force? What is Pam's final kinetic energy?

Answer 1

For #1:
Truck did more.
Consider the kinetic energy gained by each vehicle. Sine the truck is likely 10 times mor massive, using the relation
KE=1/2*m*v^2
using the factor of 10, you see that the energy is proportional to the mass. The work done by the engine is what supplied the energy.

#2
As you work with energy relationships, you will find that potential energy is
m*g*h
In a frictionless world, the kinetic energy of the rocket gets translated into potential energy, which is work against gravity:

1960=10*9.81*h

For #3, this is a classic work=force* displacement

We will assume the ice is frictionless, so the kinetic energy is equal to the force times 22m:

F*22=1/2*45*62^2

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