Forces

Question 1

what does the weight of an object depend on?

Answer 1

gravitational field strength & location of object within gravitational field

Question 2

what is a resultant force?

Answer 2

single force acting in one direction from adding or subtracting more than one force in different directions

Question 3

how do you find the resultant force of 2 forces using a scale diagram?

Answer 3

tip to tail method
put the scale
measure the direction as a bearing

Question 4

how do you find the missing force for an object in equilibrium using a scale diagram?

Answer 4

the scale diagram should form a triangle because the resultant force is 0
tip to tail method - connect the triangle
put the scale
measure the direction as a bearing

Question 5

what is elastic potential energy?

Answer 5

energy transferred to the spring as it is deformed

Question 6

what do levers & gears do?

Answer 6

multiply the effect of a turning force using moments

Question 7

why is density constant in a liquid?

Answer 7

it does not change with the shape or size of the container

Question 8

what does a submerged object experience?

Answer 8

the pressure of the fluid

Question 9

what volume of liquid does an object displace when it floats?

Answer 9

volume equal to its weight

Question 10

what happens to atmospheric pressure as altitude increases & why?

Answer 10

atmospheric pressure decreases
number of air particles & weight of air above a surface decreases because density decreases
as height increases there is always less air above a surface than at a lower height

Question 11

what is atmospheric pressure caused by?

Answer 11

air particles colliding with a surface

Question 12

what is the typical speed of cycling?

Answer 12

6m/s

Question 13

what is the typical speed of a car?

Answer 13

25m/s

Question 14

describe the acceleration of an object falling through a fluid

Answer 14

the object initially accelerates due to the force of gravity (because the force of gravity is much greater than the frictional force slowing it down)
as its speed increases, frictional force increases
this reduces acceleration until frictional force = accelerating force
so resultant force will be 0
so the object moves at its terminal velocity

Question 15

explain the shape of a velocity-time graph for a skydiver

Answer 15

when an object first sets off, the gravitational force in much higher than the frictional force so accelerate quickly
as speed increases, frictional force increases
so rate of acceleration decreases
until accelerating force = frictional force so resultant force is 0
skydiver has reached terminal velocity - maximum speed & stay at constant speed

Question 16

what is newton’s first law?

Answer 16

if the resultant force is zero, a stationary object will stay stationary & a moving object will continue moving at constant velocity (same speed & direction)

Question 17

what is inertia?

Answer 17

the tendency for an object to stay in a state of rest or uniform/constant motion

Question 18

what is newton’s second law?

Answer 18

force is directly proportional to acceleration
F=ma

Question 19

how do brakes work?

Answer 19

brake pads are pressed against tyres, causing friction, which causes work to be done

this transfers energy from kinetic energy store of car to thermal energy store of brakes so brakes increase in temperature

Question 20

what can a large deceleration cause?

Answer 20

brakes to overheat & skidding
= injury

Question 21

how do you estimate the braking force involved in deceleration of vehicle?

Answer 21

assume deceleration is uniform so use v2-u2=2as to find deceleration (a)
use F=ma with m=1000kg (estimate of mass of car)

Question 22

how does speed affect braking distance?

Answer 22

work done to stop the car = car’s kinetic energy store
E=1/2mv2
as speed doubles, kinetic energy increases 4-fold
so work done to stop car increases 4-fold
W=Fs so braking distance increases 4-fold