Units
What is the unit of force?
newton (N)
Forces can be classified as pulling forces, _______ forces and _______ forces.
pushing, twisting
Inertia of an object is only determined by the ______ of the object.
mass
There is an equation about a spring:
_________ = Extended (stretched) length - original (initial) length
What is __________ ?
extension
Write down the equation that correctly connects weight, mass and gravitational field strength.
Weight = mass × gravitational field strength
W = m × g
What is the SI unit of mass?
kilogram (kg)
Newton's First Law states that an object will stay ________ or move at _________ speed in the same direction until an external force acts on it.
stationary (still) constant
Hooke's law states that:
F = kx
What is k ?
What is x ?
k is the spring constant of the spring.
x is the extension of the spring.
True or false?
The mass of an object is different if the object is taken to Moon.
False. Mass of an object does not change due to different planets.
What is the unit of weight?
newton (N)
What can force change of an object?
shape, size, motion
Newton's Second Law states that: F = ma
What is F?
What is m?
What is a?
F is force on an object.
m is mass of the object.
a is the acceleration caused by the force.
What is the maximum load at which a spring maintains a linear relationship between load and extension?
the limit of proportionality
Moon has a smaller gravitational field strength than Earth.
How dose the mass and the weight of an object on the Moon compared to on the Earth?
same mass as on the Earth, less weight than on the Earth
What is the unit of gravitational field strength?
newton per kilogram (N/kg)
What are the three non-contact forces?
magnetic forces, electrostatic forces, gravitational forces
①How much force is required to accelerate a 2 kg mass to 3 m/s2 ?
②What is the acceleration of a 5 kg mass pushed by a 10 N force?
①6 N ②2m/s2
A spring has a spring constant k = 10 N/cm. What load is needed to produce an extension of 50 mm?
50 N
On Mars, the acceleration of free fall is 3.7 m/s2. What is the weight of a 2.0 kg mass on Mars?
7.4 N
What is the unit of spring constant?
newton per meter (N/meter) or newton per centimeter (N/cm) or newton per millimeter (N/mm)
① Weight of the rocket is 500 000 N.
② Upthrust from the engine is 1 200 000 N.
③ Air resistance is 400 000 N.
Calculate the resultant force acting on the rocket.
300 000 N, upwards
A ball is dropped in a vacuum from a height of 5.0 m above the surface of Mars. The acceleration of the ball at a height of 3.0 m is 3.8 m/s2.
What is the acceleration of the ball at a height of 0.8 m above the surface of Mars?
3.8 m/s2
A student measures the length of a spring. She then attaches different weights to the spring. She measures the length of the spring for each weight.
When no weight is attached to the spring, the length of the spring is 520 mm.
When a 8 newton weight is attached to the spring, the length of the spring is 524 mm.
What is the spring constant of this spring?
2 N/mm
In which situation in no resultant force needed?
① a car changing direction
② a car slowing down
③ a car moving in a straight line at a steady speed
④ a car speeding up
③