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### Forces and Newton’s Laws: Practice

Once again: everybody fights, nobody quits

Problem 1: OMG, they are so easy

- Newton’s 1st law:
- Newton’s 2nd law:
- Newton’s 3rd law:
- What is difference between mass and weight?

…And then…

- An airplane is flying at a constant speed. Draw a free body diagram of the plane below and include all the forces on the plane.

…And then…

- A frisbee has been thrown and is maintaining a constant altitude. Draw a free body diagram below and show all the forces acting on the frisbee.

…And then…

- A force of 20 N is acting at an angle of 500 from the horizontal.
- Find FX:
- Find FY:

…And then…

- A force of 30 N is acting at an angle of 1500 from the horizontal.
- Find FX:
- Find FY:

…And then…

- A pair of Freedom HS students find themselves having to push a stalled car. Frances Lee pushes with a force of 400 N and Kyle Cogar pushes with a force of 300 N. There is a 590N frictional force acting on the car.
- Draw a free body diagram for the system.
- Find the acceleration.
- a = 0.059m/s2

…And then…

- Jordan Lee is on a raft. He exerts a force of 17N due east by rowing and the current exerts a force of 15 N at 670. Ignoring friction, what are the X- and Y-components of the raft’s acceleration if the total mass = 1300Kg?
- aX = 0.018m/s2, aY = 0.011m/s2
- Total magnitude of acceleration?

…And then…

- A question from conceptual physics (you should totally be able to handle this one): A horse is pulling a cart. In doing so, the cart pulls on the horse with equal force. Why isn’t this a futile exercise? Why is that the horse is able to pull the cart?

….And then…

- Scott Keeler grows up to become an astronaut. While working in space, he pushes on a satellite (11,000kg) with a force of 36 N. If his mass is 92 kg, what is the force on him from the satellite? What are both object’s acceleration?
- -36N, 0.0033 m/s2, -0.39 m/s2.

….And then…

- What is the equation for the law of universal gravitation?
- What is the value of G?
- For two point masses of 20 and 25 kg separated by 3 m, what is the force of gravity they exert on each other?

….And then…

- The mass of the earth is 5.9742 × 1024 kg and the mass of the sun is 1.99 X 10 30 kg. They are separated by a distance of 146 X 109 m. What is the magnitude of the gravitational attraction on the earth by the sun?
- 3.72 X 1022 N

….And then…

- Saturn has an equatorial radius of 6 X 107 m and a mass of 5.67 X 1026 kg. What is the acceleration due to gravity at the equator of Saturn?
- 10.5 m/s2

….And then…

- What is weight?
- What is the equation for weight on the surface of earth?
- What is the difference between weight and the force of gravity on an object?
- Suppose the force of gravity on an object is 20 N when it is sitting a distance X from the center of a second object. If X is doubled, how does the force of gravity change?

….And then…

- A 12 kg object sits at rest on a table. What is its weight?
- What is the normal force on it from the table?
- If I push down on the object with an additional 6 N force, what is the normal force now from the table?
- If I pull up on the object with a 6 N force instead, what is the normal force from the table?

….And then…

- What is apparent weight?
- What is the difference between apparent weight and actual weight?
- If a 300 N man is on an elevator that is accelerating upwards at 2 m/s2, what is the man’s apparent weight?
- What about if it is descending at 2 m/s2?

….And then…

- What is the difference between static and kinetic friction?
- Write the equation for frictional force.
- If the normal force is 40 N and the coefficient of friction is 0.3, what is the frictional force?

….And then…

- State the conditions for equilibrium.
- Travis Risinger is leaning at an angle of 450 against a wall. Name all the forces at work in this system. What is the net force on Travis?
- Can you have equilibrium at constant velocity?

….And then…

- A system of masses and a pulley is show below. If there is no friction, what is the acceleration in the system?
- What is the coefficient of static friction required to keep the system at rest?

m1 = 2 kg

m2 = 3 kg

….And then…

- An object is moved from sea level to the top of Mount Everest. Which changes: mass, weight, both, or neither?
- Object 1 weighs twice as much as object 2 at the same spot on earth. Would the same be true at the same place on Mars?

….And then…

- A box is stationary on an elevator floor. Because of static friction, a force is required to get the box moving horizontally. Rank the force necessary for the situations when the elevator is stationary, accelerating downwards and accelerating upwards. Explain.

….And then…

- Two bottle rockets are launched, one pointed straight up and one pointed horizontally. Ignoring friction and air resistance, which experiences the greater acceleration? Explain.

….And then…

- A rollercoaster is accelerated from rest to 45 m/s in 7sec. The total mass of the coaster plus riders is 5.5 X 103 kg. What is the average net force exerted on the coaster?

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