# Physics

posted by .

A box with a mass of 7.00 kg is at rest on a ramp that is at an angle of 20 degrees with the horizontal. The coefficient of static friction between the box and the ramp is 0.800. Use g = 9.80 m/s2. You now want to make the box move by applying a force. To start the box moving, what is the minimum force you need to apply if your force is directed ...

(a) parallel to the slope?
.N

(b) perpendicular to the slope?
.N

(c) horizontally?

N

I know that (a) is The static friction in the x direction minus the box sliding down in the x direction, but I cannot wrap my head around the other two.

• Physics -

i have this same problem but my coefficient of friction is .7 not .8. the answer i got for a) was 21.6614. i havnt gotten b or c. the equation i used for a. was F+Fgx'=fs

• Physics -

for b, the formula I used is (if P is the perpendicular force) Fgx'=uS(Fgy'-P) (can you let me know if that is right. ive used 5 attempts before i figured out this formula and want to make sure. for , the formula i used was (if H is your horizontal force) Hx'+Fgx'=uS(Fgy'-Hy') this one is correct

• Physics -

Can you explain what Hx'+Fgx'=uS(Fgy'-Hy') means? It's hard to elaborate when the variables aren't defined.

• Physics -

same for Fgx'=uS(Fgy'-P)

• Physics -

H is your horizontal force applied. it is your unknown Since the motion is on a ramp, you have to redefine your axis. the x' axis is parallel to the ramp and the y' axis is perpendicular to the ramp. so Hx' is the x' component of the H force. Hy' is the y' component of the H force. Fgx' is the x' component of gravity. uS is your coefficient of static friction.

does that make more sense?

• Physics -

Yeah I got that, but I was hoping you could explain what you defined as the x' and y' component of each like in terms of cos and sin seeing that we might not be on the same page so i cant check ur answers exactly if i use something different.

• Physics -

also, P is the perpendicular force you apply. it is also your unknown. in the Hx'+Fgx'=uS(Fgy'-Hy')Hx'=Hcos20 and Hy'=Hsin20

• Physics -

thus you assume Fgx' is mgcos20 and Fgy' is mgsin 20?

• Physics -

no, Fgy'=mgcos20 and Fgx'=mgsin20

• Physics -

ps, i just confirmed that if you plug in the correct numbers for those equations, you will get the right answers

• Physics -

okay, just making sure

• Physics -

I am trying your equation from for P. I have a feeling it will come out as a negative force and if you apply a perpendicular force it will only increase the contact force and thus not move the box, but let me see.

• Physics -

Yes, your equation is right so if you just plug in your given numbers for P=mgcos20-(mgsin20/uS) you should get the correct answer.

• Physics -

yea, P is pushing the box away from the ramp not into it

• Physics -

yeahh

## Similar Questions

1. ### Physics

A box of textbooks of mass 25.3 kg rests on a loading ramp that makes an angle (ALFA) with the horizontal. The coefficient of kinetic friction is 0.260 and the coefficient of static friction is 0.330 . A) As the angle (ALFA) is increased, …
2. ### Physics

A 10-kg wooden box rests on a wooden ramp. The coefficient of static friction is 0.50, and the coefficient of kinetic friction is 0.30. What is the friction force between the box and ramp if the ramp is at a 25o angle?
3. ### physics

A wooden box with a mass of 10.0kg rests on a ramp that is inclined at an angle of 25 degrees to the horizontal. A rope attatched to the box runs parallel to the ramp and then passes over a frictionless pulley. A bucket with a mass …
4. ### PHYSICS

A 100-kg box is placed on a ramp. As one end of the ramp is raised, the box begins to move downward just as the angle of inclination reaches 15 degrees. What is the coefficient of static friction between box and ramp?
5. ### Phyiscs

A wooden box with a mass of 10.0kg rests on a ramp that is inclined at angle of 25 degrees to the horizontal. A rope attached to the box runs parallel to the ramp and then passes over a frictionless pulley. A bucket with a mass of …
6. ### physics

A box of mass 5.0 kg starting from rest slides down a 1.8 m long ramp inclined at an angle of 22.0 deg. from the horizontal. If the ramp is frictionless, how long will it take the box, starting from rest, to reach the bottom of the …
7. ### Phyics

A box of mass 14.0 kg sits on a horizontal steel ramp 4.8 m long with a coefficient of static friction of 0.40 between the ramp and the box. The end of the ramp is slowly lifted until the box begins to slide down the ramp. What angle …
8. ### Physics

A box of mass 54.0 kg is sitting on a ramp which makes an angle of 37.0 degrees with respect to the horizontal. The coefficient of friction between the box and the ramp is 0.21. This box is connected by a massless string over a pulley …
9. ### Physics

A block is sitting on a rough ramp. It is found that a force of F = 200.0 N (directed up the ramp) is required to keep the box from sliding back down the ramp. The angle 𝜃 is 35.0o and the mass of the box is 150.0 kg. What …
10. ### AP Physics

A mystery surprise box is sliding down a ramp at a constant speed. The box has a mass of 55.0kg and the ramp makes a 40.0œ angle with the horizontal. What is the coefficient of kinetic friction between the box and the ramp?

More Similar Questions