Gravitional Potential Energy and Elastic Potentional Energy

y201

1. The problem statement, all variables and given/known data

1) A rifle shoots a spring of mass 0.008kg and with a spring constant of 350 N/m. You wish to hit a target horizontally a distance of 15 m away by pointing the rifle at 45 degrees above the horizontal. How far should you extend the spring in order to reach the target?

2. Relevant equations
1) d=v*t, v2=v1+a*t, d=v1(t)+(0.5)(a)(t)

3. The attempt at a solution
im lost :(

1. The problem statement, all variables and given/known data

A bungee cord need to transfer 2,000,000 J of energy. A 10 kg mass extends the bungee cord 1.3m. What is the maximum extension of the bungee cord?

2. Relevant equations
F=kx, E=(0.5)(k)(x^2) W=F*d


3. The attempt at a solution
lost again :(

cupid.callin

you need to show what you've tried in the question

y201

sadly, i dont even know where to start.

AlexChandler

Try to start by finding the maximum height that the spring must reach. Then try to consider changes in energy.

y201

can you start me off with few steps please?

AlexChandler

Sure. Try to combine the kinematics equations by eliminating the time in order to reach the trajectory equation. It should look like this.

[tex] y = tan \theta_0 x - \frac{g cos^2 \theta_0}{2 V_0^2} x^2 [/tex]

Then you should be able to find the maximum height.

y201

this equation is for the second question right?

AlexChandler

No it is for the spring problem.

cupid.callin

you can also do it the traditional way

find the time of flight using y = ut + .5gt₂

now as horizontal speed donot change throughout the motion: distance you need to reach, d = u_X * t

so you have u_X viz ucos45

now use energy conservation

.5 kx² = .5m^v