Chapter 4,5,6
1) A 500-kilogram rocket is fired straight up from the earth, the engines providing 7 500 newtons of thrust. Its acceleration is
1) 5.2 meters per second squared.
2) The gravitational force on an object in motion is centripetal and constant in magnitude whenever the object is
2) In circular orbit only.
3) The gravitational field at the surface of Mars is 3.3 meters per second squared and its radius is 3 400 kilometers. When the Viking spacecraft was 3 400 kilometers above the surface of Mars, its acceleration was
3) 0.83 meters per second squared.
4) In outer space, a 250-kilogram rocket is to be speed ed up from 60 meters per second to 75 meters per second in 5 seconds. The trust needed is
4) 750 newtons
5) A force of 40 newtons keeps a rock going in a horizontal circle by means of a string 2 meters long. If the rock is moving at 10 meters per second, its mass is
5) 0.8 kilogram
Newtons first law
An object at rest will stay at rest, an object that is moving will stay moving unless disturbed by an unbalanced force.
Calculate the horizontal force that must be applied to a 1-kg puck to make it accelerate on a horizontal friction-free air table with the same acceleration it would have if it were dropped and fell freely.
F = ma = (1 kg) (9.8 m/s^2 ) = 9.8 N
Calculate the horizontal force that must be applied to produce an acceleration of 1.8 g for a 1.2-kg puck on a horizontal friction-free air table.
F = ma = (1.2 kg)(1.8)(9.8 m/s^2 ) = 21.2 N
Newtons third law
For every action, there is an equal and opposite reaction
Which of Newton's Three Laws does the following statement satisfy? Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.
Newton's first law
Which of Newton's Three Laws does the following statement satisfy? The relationship between an object's mass (m), its acceleration (a), and the applied force F is F=ma. Acceleration and force are vectors. This law requires that the direction of the acceleration vector is in the same direction as the force vector.
Newton's second law
Which of Newton's Three Laws does the following statement satisfy? For every action there is an equal and opposite reaction.
Newton's third law
Newtons second law
The "force exerted on an object equals its mass times the acceleration produced" is a description of:
Calculate in Newtons the weight of a 2000-kg elephant
W = mg - 2000 kg x 9.8 N / kg = 19,600 N
Calculate in Newtons the weight of a 2.5-kg melon. What is its weight in pounds?
W = mg = 2. Kg x 9.8 N/kg = 24.5 N; 2.5 kg x 2.2 lb = 5.5 lb
If a woman has a mass of 50 kg, calculate her weight in Newtons.
W = mg = 50 kg x 9.8 N / kg = 490 N
An apple weighs about 1 N. What is its mass in kilograms? What is its weight in pounds?
W = mg, so m = W/g = 1 N / (9/8 N/kg) = 0.1 kg; 0.22 lb
Calculate the acceleration of a 2000-kg, single-engine airplane just before takeoff when the thrust of its engine is 500 N.
a = F / m = (500 N) / (2000 kg) = 0.25 m/s^2
Calculate the acceleration of a 300,000-kg jumbo jet just before takeoff when the thrust for each of its four engines is 30,000N.
a = F / m = 4 (30,000 N) / (300,000 kg) = 0.4 m/s^2
a. Calculate the acceleration if you push with a 20-N horizontal force on a 2-kg block on a horizontal friction-free air table. b. What acceleration occurs if the friction force is 4 N?
a. a = F / m = (20 N) / (2 kg) = 10 m/s^2 ; b. a = (20 n - 4 N) / (2 kg) = 8 m/s^2
Susie Small finds she weights 300 N. Calculate her mass.
m = W/g = 300N / 9.8 N/kg = 30.6 kg
