Forces and Motion

Question 1

What is the formula for cauculating average velocity?

Answer 1

1) Velocity = Total Displacement/
Total Time
2) AverageVelocity= v initial + v final/
2

Question 2

What is the formula for cauculating average speed?

Answer 2

Speed = Distance Taken/
Time Taken

Question 3

What is the formula for cauculating acceleration?

Answer 3

Acceleration = Change in velocity/
Time Taken
a = ( v - u ) /
t

Question 4

What is the unit for momentum?

Answer 4

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).

Question 5

What is a vector quatity?

Answer 5

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.

Question 6

What is the formula for cauculating the momentum of an object?

Answer 6

p = mv
p = Momentum
m = Mass
v = Velocity

Question 7

What is the formula for cauculating the kinetic energy of an object?

Answer 7

KE= 1/2 mv^2
KE = Kinetic Energy (in joules)
m = Mass of an object (in kilograms)
v = Velocity (in meters per second)

Question 8

Calculate the momentum of a car which has a mass of 1200 kg and a velocity of 13 m/s northeast.

Answer 8

15 600 kilogram metres per second

Question 9

What is velocity?

Answer 9

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.

Question 9

What is kinetic energy?

Answer 9

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.

Question 10

Cauculate the velocity of a cyclist which has a momentum of 405 kg m/s (west), and a mass of 45 kg.

Answer 10

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).

Question 11

Why does a cannon recoil (moves backwards) when it is fired?

Answer 11

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.

Question 12

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.

Answer 12

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)

Question 13

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.

Answer 13

Velocity = 30m/s - 0m/s = 30m/s
Velocity / Time = 30m/s / 3s = 10s
50kg x 10s = 500 Newtons

Question 14

A motor lifts a 2.5 N weight 2 m. Calculate the work done on the weight.

Answer 14

W = F x dW = 2.5 x 2W = 5J
5 Joules

Question 15

What is the unit of measurment for work done?

Answer 15

It is measured in Joules

Question 16

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.

Answer 16

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

Question 17

A 3 N weight is suspended from a spring, causing the spring to extend by 4 cm. Calculate the spring constant of the spring.

Answer 17

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.