Physics of Motion

M1.2 + M1.3

What is the difference between distance and displacement?

distance is the length joining two points

displacement is the distance between an object’s initial position and its final position

An object at rest at the origin starts to move along a straight line with a constant acceleration of 5.5 m s^-2. Determine:

a)The time taken by the object to reach the displacement of 20 m

b)The velocity when the displacement is 20 m

2.7 s, 14.8 m s^-1

While driving at 40 km h^-1, Winnie see the green light turns yellow and she apply the brake immediately. Assuming a constant acceleration, if she managed to come to a complete stop after 4.8 s,

a)what is the acceleration of the car?

b)what is the stopping distance?

-2.3m/s², 26.8m

A train at rest starts to move from one station and stops at another station in 18 minutes. In the first 3 minutes, it moves with a constant acceleration of 0.20 m s^-2 and after that its velocity is constant until it is stopped by a constant force from the brakes, which is applied for 1 minute. Determine the distance between the two stations.

34.6km

A flowerpot falls off the balcony that is at a height of 8.0 m from the ground.

Determine

a)the duration of the fall

b)the final velocity of the flowerpot before it hits the ground

1.26s, 12.6m/s

The same incident in the previous slide happens in another unit. This time, the flowerpot takes 2.0 s to reach the ground.

Determine

a)the final velocity of the flowerpot before it hits the ground

b)the height of this unit

20m/s, 20m

Suppose there is a hero in a comic that is able to jump vertically to a height of 10 m above the ground using only his feet.

a)what is his initial velocity leaving the ground?

b)how long will he stay in the air?

c)what is his final velocity upon reaching the ground?

d)at what time will he reach the height of 5 m?

14.1m/s upward, √8 s, 14.1 m s^-1 downward, 0.41 s & 2.41 s

The ceiling of a classroom is 3.75 m above the floor. A student tosses an apple vertically upwards, releasing it 0.50 m above the floor.

a)What is the maximum initial speed that can be given to the apple if it is not to touch the ceiling?

b)At what time will the apple reach its maximum height?

8.1m/s, 0.8s

A person throws a stone straight upward at an initial speed of 15 m s^-1 on a bridge that is 25 m above the surface of the water. If the stone just misses the bridge on the way down,

a)what is the velocity of the stone just before it hits the water?

b)What is the total time the stone is in the air?

26.9m/s downward, 4.2s

What are the three equations for motion?

v = u + at

v² = u² + 2as

s = ut + ½ at²

What does a velocity-time graph look like?

What does a displacement-time graph look like?