EQ's Flashcards
A horse is accelerating.
It has a driving force of 2000KN
Therefore, do the friction and air resistance forces acting on the horse add up to more or less than 2000KN
[1 mark]
Less than
A horse is accelerating
The driving force acting on the horse is 2000KN. The friction and air resistance forces acting on it add up to less than 2000KN.
Is the horse accelerating or decelerating?
Explain your reasoning
[3 marks]
The horse is accelerating.
The driving force of 2000KN is greater than the forces of friction and air resistance.
Therefore the resusltant force is acting in a forward direction
In a game of tennis, a ball is hit horizontally at a speed of 40 m/s.
After 0.5 seconds, its horizontal velocity has not changed, but it has
developed a downwards component of velocity of approximately 5 m/s.
By drawing a suitable scale diagram, determine the magnitude and
direction of the tennis ball after 0.5 seconds
say how you would do this question
- draw scale diagram (triangle one to find magnitude of resultant force) using a suitable scale
- find the angle between the resultant force and the horizontal line to find the direction. direction= x degrees horizontal
A box is pushed over a rough surface at a constant velocity.
A frictional force of 4 N is acting on it.
Calculate the work which it does against friction when it is pushed through a distance of 50 cm
W=Fx s
W=?
F=4N
s=50cm - 50cm=0.5m
W= 4 x 0.5
W=2 Joules
A car is moving with a velocity of 20 m/s.
The driver applies the brakes and the car comes to a stop
Describe the energy transfers in the car when the brakes are applied
[4 marks]
When the brakes are applied, a frictional force acts between the floor and the wheels
The kinetice energy store or the car is transferred to the thermal energy store of the brakes.
This causes the temperature of the breaks to increase.
The car slows down and the kinetic energy is dissipated into the surrounings
Describe the
relationship between the force and the extension when the limit of proportionality has been exceeded
[2 marks]
The relationship is non-linear
as the extension is no longer directly proportional to the force applied
Thom is carrying out an experiment to see the relationship between force and extension within the limit of proportionality.
He made a mistake when measuring the extension for each applied force.
Suggest a mistake he may have made.
[1 mark]
He measured the total length of the spring instead of its extension
An object is at rotational equilibrium
The distance on he right side of the pivot is decreased
Suggest why the counterbalance on the left side of the pivot should be adjusted
[2 marks]
The clockwise moment being exerted is decreased
Unless the counterbalance is adjusted there will be a resultant force
So the object will topple over
Explain why an ice cube will float and then come to a state of rest when a force is removed from it
[3 marks]
When the downwards force acting on the object, the magnitude of the upthrust is greater than the weight exerted on the cube
This means that there will be a resultant force acting upwards on the ice cube
Causing the cube to accelerate upwards.
When the upthrust equals the weight of the ice cube then the ice cube will remain at rest
A boy is walking through a forest.
Explain why his speed at a given point in time will not be the same as his average speed for the entire journey
[2 marks]
The boy may have walked faster or slower at different points of the journey and may have stopped walking atcertain points
The average speed is the total distance travelled divided by the total time taken so this would not take these changes into account
Explain why an object being dropped on the moon will have a different velocity than an object dropped on earth
[3 marks]
On the moon there is no atmosphere on the earth there is an atmosphere
This atmosphere means that as the objects falling on the earth will experience an upwards force of air resistanct acting in the opposite direction to its motion
This will cause the downwards resultant force to decrease and so the acceleration of the object will decrease too
A student moved beaker A (empty) and beaker B filled with water, applying the same force to each of them.
Explain why beaker A moved further than beaker B
[2 marks]
Beaker A has a smaller inertial mass than beaker B
This means that it will the greater acceleration when the same force applied to each of them
as a= F/m
the smaller the m the bigger the a with the same F
Explain, making reference to Newton’s third law, how the force of friction allows us to walk across a surface.
[2 marks]
When we walk forwards we push our feet backwards
After this, by Newton’s third law, an equal and opposite force of friction from the ground is exerted onto our feet and pushes them forwards allowing us to walk.
An iceskater is standing at rest and then throws a tennis ball.
Explain why (according to the law of the conservation of momentum) the iceskater moves backwards after she throws the ball
[3 marks]
Before the iceskater throws the ball, she is at rest to the total velocity is 0.
After she throws the ball, the forward momentum of the ball increases
By the conservation of momentum, the iceskater backwards momentum of the iceskater increases and it equal to the forwards momentum of the ball so they balance and the total momentum after the event it 0.
Two cars collide with eachother.
The total momentum before the collision was 90,000kgm/s
The total momentum after was 75,000kgm/s
Compare and comment on the two momentums
[3 marks
The total momentum before was greater than the total momentum after
This means that the collision did not occur in a closed system
And there must have been some external forces acting on the two cars like friction
