Forces and Motion Flashcards
(25 cards)
What is the formula for cauculating average velocity?
1) Velocity = Total Displacement/
Total Time
2) AverageVelocity= v initial + v final ÷ 2
What is the formula for cauculating average speed?
Speed = Distance Taken ÷ Time Taken
What is the formula for cauculating acceleration?
Acceleration = Change in velocity ÷ Time Taken
a = ( v - u ) ÷ t
What is the unit for momentum?
Kilogram meter per second (kg m/s)
Since momentum is calculated by multiplying the mass by the velocity, we can see that the units for momentum can be deduced by multiplying the units for mass (kilograms) by the units for velocity (metres per second).
What is a vector quatity?
A vector quantity is a physical quantity that has both magnitude (size or amount) and direction. This means that to fully describe a vector quantity, you must specify how large it is and the direction in which it acts.
What is the formula for cauculating the momentum of an object?
p = mv
p = Momentum
m = Mass
v = Velocity
What is the formula for cauculating the kinetic energy of an object?
KE= 1/2 mv^2
KE = Kinetic Energy (in joules)
m = Mass of an object (in kilograms)
v = Velocity (in meters per second)
Calculate the momentum of a car which has a mass of 1200 kg and a velocity of 13 m/s northeast.
15 600 kilogram metres per second
What is velocity?
Velocity specifies both how fast an object is moving and in which direction. For example, “50 m/s north” is a velocity, while “50 m/s” is just a speed. A positive velocity indicates motion in a chosen positive direction. A negative velocity indicates motion in the opposite direction.
What is kinetic energy?
Kinetic energy is the energy an object possesses due to its motion. It depends on both the mass of the object and the square of its velocity. Kinetic energy is always a positive value because mass and the square of velocity are always positive.
Cauculate the velocity of a cyclist which has a momentum of 405 kg m/s (west), and a mass of 45 kg.
The first stage in answering this question is to rearrange the equation for momentum to make velocity the subject of the equation. Divide both sides by mass. Then you can substitute the values for momentum and mass into the rearranged equation. The answer is 9 m/s (west).
Why does a cannon recoil (moves backwards) when it is fired?
When the cannon is fired, the explosive force propels the cannonball forward with a certain amount of momentum. According to the law of conservation of momentum: Totalmomentumbeforefiring
= Totalmomentumafterfiring.
A red toy car has a mass of 0.1 kg and a velocity of 3 m/s to the right. It collides with a blue toy car which has a mass of 0.2 kg and which is moving at a velocity of 1 m/s to the left. The two cars stick together after the collision. Calculate their velocity after the collision.
Momentum = Mass × Velocity
Red car: Momentum = 0.1 × 3
Momentum = 0.3 kg m/s
Blue car: Momentum = 0.2 × -1
Momentum = -0.2 kg m/s
Total Momentum = 0.3 + (-0.2)
Velocity = 0.1 ÷ 0.3
Velocity after collision = 0.33 m/s (to the right)
A cheetah has a mass of 50 kg and it accelerates from rest to a speed of 30 m/s in 3 seconds. Calculate the force which accelerates the cheetah.
Velocity = 30m/s - 0m/s = 30m/s
Velocity / Time = 30m/s / 3s = 10s
50kg x 10s = 500 Newtons
A motor lifts a 2.5 N weight 2 m. Calculate the work done on the weight.
W = F x dW = 2.5 x 2W = 5J
5 Joules
What is the unit of measurment for work done?
It is measured in Joules
A saucepan containing 4.5 kg of water is heated from 20 °C to 100 °C. Given that the specific heat capacity of water is 4200 J/kg°C, calculate the energy transferred to the water.
ΔE = m × c × ΔθΔE = 4.5 × 4200 × (100 – 20)
ΔE = 4.5 × 4200 × 80
ΔE = 1,512,000 J
(Note that the temperature difference is 80 °C, which is calculated by subtracting the initial temperature (20 °C) from the final temperature (100 °C).)
1,512,000 Joules is transferred to the water
A 3 N weight is suspended from a spring, causing the spring to extend by 4 cm. Calculate the spring constant of the spring.
k = F ÷ ek = 3 ÷ 0.04k = 75 N/m
Note that the extension of 4 cm must be first converted to metres (to do this divide the value by 100, giving an extension of 0.04 m) before substituting the values into the formula. The spring constant is 75 N/m.
What is torque and what is it measured in?
Torque is a the twisting or turning force that causes an object to rotate around a fixed pivot point or axis, and it is measured in Newton meter (Nm)
What is the typical distance measured in?
Meters per second (m/s)
A line graph shows a car’s speed while traveling down a road. The car is _________________, shown by the line getting steeper and the gradient getting bigger.
Accelerating
A line graph shows a car’s speed while traveling down a road. The car is _________________, shown by the line getting flatter and the gradient getting smaller
Decelerating
A _____ is a quantity that has both size and direction
Vector
A car of mass 2000 kg hits the ground travelling at 40 m/s. It is brought to rest in 0.02 s. What is its accerleration? What is the consequence of such a rapid deceleration?
a = ( v - u ) ÷ t
a = (0 m/s - 40 m/s) ÷ 0.02 s
a = -40 m/s ÷ 0.02s
Accerleration = -2000 m/s^2
F = m x a
F = 2000 kg x 2000 m/s^2
The car experiences 4,000,000 N of recoil force and instantly become completely crushed and everyone inside will die.
