# Any Hints?

1. Sep 29, 2004

### Fused

Any Hints!?!?

I'm stuck on these 2 problems.. Any hints would be helpful!

1. What is the minimum work needed to push a 950-kg car 810m up along a 9 degree incline? a) ignore friction, b) assume the effective coefficient of a friction retarding the car is .25.

This is what I did, but I don't think it's correct... :
A) W= Fdcost = mdcost = (950)(810cos9) = 7.6 * 10^5 J.
B) Wfr= Ffr*x*cos(180+9) = .25 * 810 *cos189 = -200 J

2. A 65 kg trampoline artist jumps vertically upward from the top of a platform with a speed of 5 m/s. A) how fast is he going as he lands o nteh trampoline, 3 m below? b) if the trampoline behaves liek a sprign with spring stiffness constant 6.2 * 10 ^4 N/m how far does he depress it?
I got the a) part using .5mv^2 + mgy1 = .5mv^2 + mgy2
and found v= 9.15 m/s
b) I'm not sure which equation to use... I tried using .5mvi^2 + .5kx1^2 = .5mvf^2 + .5kx2^2 But I wasn't quite sure what to plug in, and when I tried all the different possibilities I did not get the corect answer.

2. Sep 29, 2004

### Fused

Nobody!?! Please help! I have a quiz this friday! I really need to know how to do these problems!!!

3. Sep 29, 2004

### Pyrrhus

Fused do a Free body diagram for the body on the incline.

4. Sep 30, 2004

### Fused

I did that, but I don't know how to put the information into formulas

5. Sep 30, 2004

### Pyrrhus

Use Newton's 2nd Law

$$\sum^{n}_{i=1} \vec{F}_{i} = m \vec{a}$$