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?