Dynamics

Question 1

What are non-contact forces

Answer 1

Forces that do not require objects to be in contact to exist.
Examples: gravitational force, electrostatic force, magnetic force

Question 2

What are contact forces

Answer 2

Forces that exists between objects that are in contact
Examples; Friction, air resistance, normal force, tension

Question 3

What is the formula for gravitational field strength

Answer 3

g = W/m where g is field strength, W is weight in newtons, m is mass in kg

Question 4

When a spaceship travels between earth and moon, why does it experience zero weight at a point in time while travelling

Answer 4

The gravitational field of the Earth and Moon cancel each other

Question 5

What apparatus should be used to measure mass

Answer 5

Beam balance or calibrated electronic balance

Question 6

What apparatus should be used to measure weight

Answer 6

Spring balance

Question 7

What is the equation for force

Answer 7

F = ma

Question 8

What is Newton’s First Law of Motion

Answer 8

Every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it

Question 9

What is Newton’s Second Law of Motion

Answer 9

The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. The object accelerates in direction of net force

Question 10

The larger the mass, the ___ inertia the object will have

Answer 10

More

Question 11

Using ideas about inertia, explain why people should wear seatbelts

Answer 11

If a driver suddenly applies the brakes, he will continue to move forward due to his inertia

Question 12

What is Newton’s Third Law of Motion

Answer 12

If body A exerts force AB on body B, the body B will exert and equal and opposite force BA on body A

Question 13

What are some positive effects of friction

Answer 13

Walking, slowing down objects, grip –>prevents skidding or to hold a pen

Question 14

What are negative effects of friction

Answer 14

Wear and tear, unwanted slowing down or stopping of motion, generates unwanted heat

Question 15

How to reduce friction

Answer 15

Use smooth and polished surface
Use wheels and rollers
Use ball bearings around axles
Use lubricants
Use air as cushion
Adopt a streamline shape

Question 16

How do objects fall with air resistance

Answer 16

On earth, falling objects always experience air resistance. Air resistance increases as speed of falling object increases. At point where air resistance equals weight, there is zero acceleration and object falls with constant velocity known as terminal velocity

Question 17

Describe skydiver falling with air resistance with parachute first closed

Answer 17

When skydiver slides out from plane, only force acting is gravitational force and initial downward acceleration is uniform at 10 ms-2. As he falls, air resistance opposing motion starts to increase, net force downwards decreases and falls at decreasing acceleration. Air resistance continues to increase until it is equal to weight and he falls with zero acceleration and terminal velocity

Question 18

Describe skydiver falling with air resistance when parachute opens midway through fall

Answer 18

Skydiver opens the parachute, larger surface area of parachute gives rise to larger air resistance. Net force is upwards and skydiver decelerates. Skydiver slows down until air resistance decreases until balancing his weight. A lower terminal velocity is reached and skydiver continues to the ground at constant velocity

Question 19

How does greater weight affect terminal velocity

Answer 19

Larger weight needs larger air resistance to balance its weight. Accelerates for longer duration and larger terminal velocity, so reaches ground in shorter time due to larger average speed

Question 20

How does larger surface area affect terminal velocity

Answer 20

Object that has larger surface area traps more air molecules underneath as it falls. Air resistance increases at faster rate but final air resistance is equal regardless of surface area as weight is equal. Accelerates for shorter duration and smaller terminal velocity, so reaches ground in longer time due to smaller average speed

Question 21

Explain why ball experiences constant acceleration during free fall through air (no air resistance)

Answer 21

As there is no air resistance, the net force, the ball’s weight, remains constant and thus acceleration remains constant with mass.