P2 - Forces

Question 1

What is the difference between scalar and vector quantities?

Answer 1

Scalar - quantities that are only a number
eg. speed, mass

Vector - quantities that have a direction as well
eg. velocity, force, acceleration

Question 2

What does a diagonally line represent on a distance-time graph?

Answer 2

steady speed

Question 3

What does a horizontal line represent on a distance-time graph?

Answer 3

stopped

Question 4

How can you measure the gradient of a curve?

Answer 4

draw a tangent to the curve

gradient (of tangent) = vertical change
————————-
horizontal change

Question 5

What does a diagonal line represent on a velocity-time graph?

Answer 5

constant acceleration / deceleration

Question 6

What does a horizontal line represent on a velocity-time graph?

Answer 6

steady velocity

Question 7

An object with a zero resultant force will be…

Answer 7

in equilibrium - stationary or moving at a steady speed

Question 8

A non-zero resultant force means…

Answer 8

the forces are unbalanced and the object will either accelerate or decelerate

Question 9

How can you use scale drawings to find the resultant force?

Answer 9

draw the forces acting on the object

make sure they are to scale, pointing the right way and are “tip-to-tail”

draw the line from the first force to the last force

the length is the resultant force

Question 10

Newton’s first law

Answer 10

An object will remain stationary or at a constant velocity unless acted on by an external force

Question 11

Newton’s second law

Answer 11

The force acting on an object is equal to its rate of change of momentum

Question 12

What is terminal velocity and how is it reached?

Answer 12

At first, objects have more driving force than resistance so they accelerate

resistance is directly proportional to the velocity

so as velocity increases, resistance increases

which reduces acceleration until the friction is equal to the driving force

the forces are balanced so this is the terminal velocity

Question 13

What is inertia?

Answer 13

how difficult it is to change an objects velocity

Question 14

What is inertia dependant on?

Answer 14

the mass of the object

the larger the mass, the greater the inertia and the harder it is to change velocity

Question 15

Newton’s third law

Answer 15

When two objects interact, the forces they exert on each other are equal and opposite

Question 16

law of conservation of momentum

Answer 16

In a collision where no other external forces act, momentum is conserved

Question 17

Ball A (mass = 0.08kg) is moving at 9m/s towards ball B (mass = 0.36kg).

Ball B is moving at 3m/s in the same direction as ball A.

The balls collide. After the collision, ball A is stationary and ball B moves away.

What is the new velocity of ball B?

Answer 17

total momentum before
= (0.08 x 9) + (0.36 x 3)
= 1.8 kg m/s

total momentum before = total momentum after

total momentum after

 1. 8 = (0.08 x 0) + (0.36 x velocity B)
 1. 8 = 0 + (0.36 x velocity B)

velocity B = 1.8 = 5m/s

                 - -------
                  0. 36

Question 18

What is an elastic collision?

Answer 18

where the total energy in the kinetic stores of the objects colliding is conserved

Question 19

What is an inelastic collision?

Answer 19

where some of the energy in the kinetic energy stores is transferred to other stores

eg. transferred away by heating or by sound