Projectile Motion

Question 1

Describe object falling with air resistance from rest

Answer 1

When object is released, initial velocity is zero, so air resistance is zero, acceleration is g. As object falls, velocity increases and air resistance increases, the resultant force downwards decreases so acceleration decreases but it’s still getting faster. Air resistance will increase to value equal to weight, so resultant force becomes zero, a becomes zero and object falls at constant terminal velocity.

Question 2

Explain trajectory of object thrown vertically up in the air

Answer 2

Initial velocity is high, air resistance is high. W and R acts in same direction downward, causing deceleration > g. As object rises, v decreases and R decreases. At top, v=0 so R=0, a=g. As object falls, R and W are in opposite directions so a<g. As object’s v increases, R increases to value =W so resultant force becomes 0, a becomes 0 and object falls at terminal velocity

Question 3

Explain energy change during object falling with air resistance (in terms of energy stores)

Answer 3

As object experiences air resistance while falling, energy in gravitational store of object is transferred to kinetic store of object and transferred mechanically to internal store of surrounding air

Question 4

Explain energy change during object falling with air resistance( in terms of types of energy)

Answer 4

As an object experiences air resistance while falling, GPE is converted to KE of the object, resulting in increase in speed, and converted to heat due to friction with air molecules.

Question 5

Explain decrease in speed as skydiver opens parachute during fall in terminal velocity

Answer 5

Parachute provides larger surface area and hence experiences larger air resistance. Air resistance is larger than the weight so skydiver slows down after parachute opens.