PHYSICS 10 Lecture Notes - Lecture 3: Isolated Point, Net Force

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18 Apr 2017

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Friction and newton"s 1st law- an object will remain in motion (or at rest) if no other forces act on it, but in the real world, friction almost always acts on moving objects. Newton"s 2nd law- , where f is force and m is mass. Newton"s 3rd law- every action has an equal and opposite reaction. Objects in equilibrium- the sum of all forces is zero. Example- an astronaut has a mass of 70 kg on earth. When he has been in space for a while, his force is 130 n and is accelerated to 2 m/s2. Elevator example- accelerates upward( which we are choosing as the positive direction) at 1 m/ Dynamics- study of the forces that cause objects and systems to move. Force- a push or a pull on an object that has both direction and magnitude (a vector quantity) Free-body-diagram- a technique used to illustrate all the external forces acting on a body.

Related Questions

A space habitat for a long space voyage consists of two cabins eachconnected by a cable to a central hub. The cabins are set spinningaround the hub axis, which is connected to the rest of thespacecraft to generate artificial gravity.

(a) What forces are acting on an astronaut in one of thecabins?

(b) Write Newton's second law for an astronaut lying on the "floor"of one of the habitats, relating the astronaut's mass m, hisvelocity v, his radial distance from the hub r, and the normalforce n.
Newton's 2nd Law= ?
Normal Force= ?

(c) What would n have to equal if the 65.0-kg astronaut is toexperience half his normal Earth weight?

(d) Calculate the necessary tangential speed of the habitat fromNewton's second law.

(e) Calculate the angular speed from the tangential speed.

(f) Calculate the period of rotation from the angular speed.

(g) Calculate the tangential speed at the top of his head if he is2.08 m tall.

hi,
i have 5 questions i need the complete solutions with theirfinalresults. is there anyone could help me, i wouldappreciatethat.

1)A worker pushes a sled with a force of 40 N over a leveldistanceof 6.0 m. If a frictional force of 24 N acts on thewheelbarrow ina direction opposite to that of the worker, what network is doneon the wheelbarrow?

2) A horizontal force of 200 N is applied to a 55-kg cart acrossa10-m level surface. If the cart accelerates at 2.0 m/s2, thenwhatis the work done by the force of friction as it acts to retardthemotion of the cart?

3) If both mass and velocity of a ball are tripled, thekineticenergy is increased by a factor of:
a) 9, b) 12, c) 3, d) 6

4) A 1 200-kg automobile moving at 25 m/s has the brakesappliedwith a deceleration of 8.0 m/s2. How far does the car travelbeforeit stops?

5) Samantha pushes a 50-N crate up a ramp 25.0 m in lengthandinclined at 10Â° with the horizontal. What potential energychangedoes the crate experience?

thank you in advance

1.

While helping a friend move, you push a 11.5 kg dolly with a forceof 11.0 N. Assume there are no other forces acting on the dolly. Ifthe dolly starts at rest, how far does it move in 3.50 s?
1 m

2.

At a lumberjack competition an axe with a mass of 1.25 kg is thrownat a target with a speed of 41 m/s. When it hits the target, itpenetrates to a depth of 0.055 m.
(a) What was the average force exerted by the target on theaxe?
1 N

(b) If the mass of the axe is halved, and the force exerted by thetarget on the axe remains the same, by what multiplicative factordoes the penetration depth change?
2
It doubles. It increases by a factor of the square root of two. Itdoes not change. It decreases by a factor of the square root oftwo. It halves.
Your work in question(s) will also be submitted or saved.
3

Your 1500 kg car pulls a 540 kg trailer away from a stop sign withan acceleration of 2.00 m/s2. (Note the answers should be given inkN.)
(a) What is the net force exerted by the car on the trailer?
1 kN

(b) What force does the trailer exert on the car?
2 kN

(c) What is the net force acting on the car?
3 kN

4.

Two boxes sit next to, and touching, each other on a frictionlesshorizontal surface. The lighter box has a mass of 5.31 kg and theheavier box has a mass of 7.29 kg.
(a) Find the contact force between these boxes when a horizontalforce of 6.1 N is applied to the light one.
1 N

(b) If the 6.1 N force is applied to the heavy box instead, is thecontact force between the boxes the same as, greater than, or lessthan the contact force in part (a)?
2

(c) Verify your answer to part (b) by calculating the contact forcein this case.
3 N

5.

A child sits in a wagon and together they have a mass of 25 kg. Thewagon is pulled with a constant speed by a handle that is at anangle of 22Â° above the horizontal. If the normal force exerted onthe wagon is 210 N, what is the force F applied to thehandle?
1 N

6.

An object acted on by three forces moves with constant velocity.One force acting on the object is in the positive x direction andhas a magnitude of 6.7 N; a second force has a magnitude of 4.5 Nand points in the negative y direction. Find the direction andmagnitude of the third force acting on the object.
1 N
2Â° (counterclockwise from the +x axis)

7.

A chain is used to lift a 1200 kg car vertically upward with anacceleration of 0.90 m/s2. What is the tension in the chain?
1 N

8.

A 22.5 kg box (m1) rests on a table.

(a) What is the weight of the box?
1 N
What is the normal force acting on it?
2 N (upward)
(b) A 12.5 kg box (m2) is placed directly on top of the 22.5 kgbox.
Determine the normal force that the table exerts on the 22.5 kgbox.
3 N (upward)
Determine the normal force that the 22.5 kg box exerts on the 12.5kg box.
4 N (upward)

9.

Your friend has a weight of 127 lb when standing on a scale. Youtake the scale to an elevator where you notice your friend's weighton the scale reads 108 lb. What are the direction and magnitude ofthe elevator's acceleration?
Direction 1
Magnitude 2 m/s2

10.

When you lift a package with a force of 82 N, the packageaccelerates upward at a rate of a. If, instead, you lift with aforce of 93 N, the package now has an acceleration of 8 multipliedby a.
(a) Find the weight of the package.
1 N

(b) Find the acceleration a.
2 m/s2

11.

One 3.1 kg paint bucket is hanging by a massless cord from another3.1 kg paint bucket, also hanging by a massless cord, as shownbelow.

(a) If the buckets are at rest, what is the tension in eachcord?
(lower cord) 1 N
(upper cord) 2 N

(b) If the two buckets are pulled upward with an acceleration of1.30 m/s2 by the upper cord, calculate the tension in eachcord.
(lower cord) 3 N
(upper cord)5

12)
Your friend has a pair of fuzzy dice with a mass of 1.32 g hangingfrom his rear-view mirror.
(a) When he accelerates from a stoplight, the dice deflect backwardtoward the rear of the car hanging at an angle of 6.18Â° relative tothe vertical. Find the tension in the string holding thedice.
N

(b) At what angle to the vertical will the tension in the string betwice the weight of the dice?
Â°

PHYSICS 10 Lecture Notes - Lecture 3: Isolated Point, Net Force

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