Explain why an object falling vertically through still air reaches a constant velocity.
- gravity causes the object to accelerate, initially (1)
- resistive forces increase as the object speeds up (1)
- resistive forces eventually equals weight of the object(1)
- resultant force is now zero (1)
- therefore no more acceleration (1)
Explain why if two objects fired at the same point, the object with less horizontal velocity will travel a less distance
- their vertical motion is independent of their horizontal motion
- the acceleration due to gravity is the same for both
- for the same time.
- Distance is proportional to horizontal speed
Explain the shape of the graph in Figure 4. Your account should include:
- l how the velocity and acceleration of the steel ball vary with time
- l reference to how Newton’s First and Second laws of motion apply in this
situation.
• velocity increases and then becomes constant due to terminal velocity • acceleration reduces to zero • forces become balanced • as weight and friction are balanced • drag force increases with speed • resultant force causes acceleration • acceleration = gradient • acceleration is maximum (9.81) at the beginning
In a velocity-time graph how can you calculate the displacement of the object?
the displacement is equal to the area enclosed by the graph and the time axis
Why is the distance travelled by the train is different from its displacement
distance is a scalar and is represented by the total area under both the positive and negative portions of the graph
State Newton’s first law
an object tends to remain in constant motion unless a resultant force is acted on it
State Newon’s second law
the acceleration of an object is proportional to the force exerted on it F = ma
State Newton’s third law
for every action there is an equal and opposite reaction
State and explain how the horizontal forward force on a vehicle has to change constant acceleration to be maintained
- Has to increase
- because air resistance increases with speed
- so the forward force must be greater than resistive force
- so that the resultant force stays same
State and explain how the horizontal forward force on a vehicle has to change constant acceleration to be maintained
- Has to increase
- because air resistance increases with speed
- so the forward force must be greater than resistive force
- so that the resultant force stays same
Explain why using an inclined plane rather than free fall is more valid
- Free fall is too quick
- Galileo had no accurate method to time free fall
- No airs resistance using an inclined plane
Name and briefly describe the 2 car features ( VB and CZ)
- Vehicle bumpers (front and back): give way in a low speed impact so increase impact time and so reduce impact force
- Crumple zones: Designed to give way and crumple in front end impact so increase impact time and so reduce impact force
Name and briefly describe 3 car features
- seat belts: in a front end impact, the restraining force on the wearer, when the vehicle is suddenly stopped, is less than the impact force would be if the person, without the seat belt, hit the vehicle frame. So the wearer is stopped more gradually with than without the seat belt.
- collapsible steering wheel: if the driver makes contact, in a front end impact, with the steering wheel, the impact force is lessened as a result of the steering wheel collapsing in the impact
- airbags: reduces the force on a person, because the airbag acts as a cushion and reduces the impact time on the person. Also, the force of the impact is spread over the contact area, which is greater than the contact area with a seat belt. So the pressure on the body is less
What is the definition for impulse
The force x the time for which the force acts
