Mechanics

Two-Dimensional Motion and Trajectories

100

Compared to the force needed to start sliding a crate across a rough level floor, the force needed to keep it sliding once it is moving is A) less than B) greater than or C) the same

A) less than

200

A car starts from rest and accelerates uniformly over a time of 5.21 seconds for a distance of 110 m. Determine the acceleration of the car.

a = 8.10 m/ s2

300

A race car accelerates uniformly from 18.5 m/s to 46.1 m/s in 2.47 seconds. Determine the acceleration of the car and the distance traveled. (Hint: First find acceleration)

A=11.2m/s2 D=79.8m

400

If a stone throw from a bridge strikes the water 10.0 meters below after 1.70 secs, what was the stone's initial velocity?

2.45 m/s

500

The Roadrunner and Wile E. Coyote, who weighs twenty times more than the bird, both run off a cliff edge over a level valley at the same speed. If they remain in free fall will they; A) both hit the ground approximately at the same time, B) the bird will travel 20x the horizontal distance from the cliff than the coyote, C) the coyote travels 20x the horizontal distance from the cliff than the coyote

The correct answer is A. The horizontal velocity of a projectile is constant and all objects fall with the same acceleration rate in the absence of air resistance.

Circular Motion and Gravity

100

Identify the type of force which causes the moon to orbit the earth.

Gravity

200

A particle is moving around in a circle of radius R=1.5m with a constant speed of 2m/s. What is the centripetal acceleration of the particle?

2.67 m/s^2

300

Using Newton's Law of Gravitational Attraction, a mass of earth equal to 5.9736x10^24 kg, and an orbital period of 23 hours, 56 minutes, 4.0916 seconds, calculate the radius R of a geostationary orbit around the earth.

42164 km

400

On the surface of Earth, a spacecraft has a mass of 2.00x10^4 kilograms. What is the mass of the spacecraft at a distance of one Earth radius above Earth's surface?

2x10^4kg

500

Centrifugal means "center-seeking." True or False?

False

Friction

100

Where on the reference table can you find the table for coefficient of friction?

The front in the bottom right hand corner.

200

A projectile launched at an angle of 45 degrees above the horizontal travels through the air. COmpared to the projectile's theoretical path with no air friction, the actual trajectory of the projectile with air friction is A) lower and shorter, B) lower and longer, C) higher and shorter or D) higher and longer

A) lower and shorter.

300

A car's performance is tested on various horizontal road surfaces. The brakes are applied, causing the rubber tires of the car to slide along the road without rolling. The tires encounter the greatest force of friction to stop the car on: A) dry concrete, B) dry asphalt, C) wet concrete, D) wet asphalt. (Hint: check your reference table!!!)

A, to obtain the greatest force of friction, we'll need the greatest coefficient of friction (mu). Since the tires are sliding, we need the kinetic coefficient of friction.

400

A block of mass M = 10 kg is sitting on a surface inclined at angle θ = 45°. Given that the coefficient of static friction is μs = 0.5 between block and surface, what is the minimum force F necessary to prevent slipping? What is the maximum force F that can be exerted without causing the block to slip?

Answer: Fmin = 34.65 N, Fmax = 103.94 N The minimum force required to prevent slipping is the minimum force that will prevent the block from sliding down the incline. It is Fmin = 10gsin(45°)—10gcos(45°)x0.5. The maximum force that can be exerted without causing the block to slip is the maximum force that can be exerted without causing the block to slide up the incline. It is Fmax = 10gsin(45°)+10gcos(45°)x0.5.

500

A uniform ladder of length L is leaning against the side of a building, as shown. A person of mass m = 75 kg is standing on it. The mass of the ladder is M = 10 kg. The coefficient of static friction between the ground and ladder is μs1 = 0.5, and the coefficient of static friction between the wall and ladder is μs2 = 0.3. What is the minimum angle θ so that the ladder doesn't slip?

θmin = 61.8°

Momentum

100

A cannon fires a cannonball and recoils backward. Which of the following statements is true about the cannon recoil? A. It happens because the energy of the system is conserved B. It happens because the energy of the system is increased C. It happens because the momentum of the system is not conserved D. It happens because the momentum of the system is conserved E. It happens because the momentum of the system is increased

D. It happens because the momentum of the system is conserved

200

A freight car of mass 20,000 kg moves along a frictionless level railroad track with a constant speed of 15 m/s. What is the momentum of the car?

300,000 kg·m/s

300

A 500 kg sailboat moves with a momentum of 150,000 kg·m/s? What is the velocity of the boat?

300 m/s

400

A loaded freight car A with a mass of 24,000 kg moves at a constant velocity of 8 m/s on a horizontal railroad track and collides with an empty stationary car B with a mass of 8,000 kg. After the collision the cars stick to each other and moves like one object. What is the velocity of two cars after the collision?

6 m/s

500

A 40 kg skateboarder runs at a constant velocity of 12 m/s and jumps to a stationary skateboard with a mass of 8 kg. What is the velocity of the skateboard after the jump?

10 m/s