HDE Section 2: Motion

Question 1

What is meant by a vector quantity?

Answer 1

A vector quantity has both magnitude and direction

Question 2

Calculate the displacement of an object that travels with an average velocity of 4.5ms^-1 for 8.0s.

Answer 2

distance = average velocity x time = 4.5 x 8 = 36m

Question 3

The velocity of a car changes from 36kmph to 18kmph in 8.0s. What is the acceleration?

Answer 3

36kmph = 10ms^-1
18kmph = 5ms^-1

-5/8 = 0.63ms^-2 (Decelerating)

Question 4

What do the symbols in suvat stand for?
s =
u = 
v =
a =
t =

Answer 4

s = distance moved
u = initial velocity
v = final velocity
a = acceleration
t = time

Question 5

What is Instantaneous velocity

Answer 5

Instantaneous velocity: velocity at a given point

Question 6

What is Average velocity

Answer 6

Average velocity: can be found using (u + v)/2 (if acceleration is constant)

Question 7

In an experiment, a trolley runs down an inclined plane. An interrupter card of length 20.0cm cuts through light gates close to the top and the bottom of the slope. The following results were recorded from such an investigation. Time to cut the top gate, t1 = 0.30s Time to cut the bottom gate, t2 = 0.14s Time to travel between the gates, t = 0.50s
Calculate:
a) the velocity of the trolley at each gate
b) the acceleration of the trolley.

Answer 7

x

Question 8

A train starts from rest at a station and accelerates at 0.2ms^-2 for one minute until it clears the platform.

Calculate the velocity of the train after this time, and the length of the platform.

The train now accelerates at 0.4 m s 2 for the next 540m.
Calculate its final velocity

Answer 8

12ms^-1
360m

24ms^-1

Question 9

Explain why the quantities u, v, a and s must be vectors for rectilinear motion.

Answer 9

Rectilinear means that the quantities are all along the same line, so they have a specified direction.

Question 10

Calculate the acceleration of an object that increases in velocity from 2.0m s-‘ to 5.0ms-1 in 0.5s.

Answer 10

6

Question 11

How long will it take a dog running at 4.0ms-1 to increase its velocity to 6.0ms-1 if it accelerates at 0.8m s-1?

Answer 11

2.5

Question 12

How far will a car travel when it accelerates at 0.5 m s-2 from rest for 20 s?

Answer 12

100

Question 13

Calculate the final velocity of a cyclist who accelerates at 0.8ms-2 from an initial velocity of 5.0 m s-‘ over a distance of 12m.

Answer 13

6.6

Question 14

A ball is thrown vertically upwards with an initial velocity of 10 m s-‘. Calculate the maximum height it will reach above its starting position, and the time it will take to reach this height.

Answer 14

At the instant the ball is at its maximum height, its velocity will be zero. 
s =?,
u = +10ms^-1, 
v = 0ms^-1 ,
A= -9.8ms^-1,
t =? 

Using v^2 = u^2 + 2as: 0 = (+10)^2 + 2 x (-9.8) x s
100 = 19.6 x s
s = 5.1 m

Using v= u+at:
0 = 10ms + (-9.8) x t
t = 1.0s