Question

1. A car accelerates from 20 m/s to 40 m/s in 5 seconds. What is its acceleration?





2. A motorbike speeds up from a standing start (that is, 0 m/s) to 30 m/s in 4 seconds. How fast is its acceleration?





3. When she sees the red traffic light, Marie brakes to a halt from a speed of 70 meters per second in just 2 seconds. What is her deceleration?





4. A car traveling at 15 m/s starts to decelerate steadily. It come to a complete stop in 10 seconds. What is its acceleration?





5. A roller coaster is moving at 25 m/s at the bottom of a hill. Three seconds later it reaches the top of this hill moving at 10 m/s. What was the acceleration of the coaster?

Answer 1

Explanation:

Acceleration is a measure of the change in velocity over time. The cars change in velocity is 40m/s−20m/s=20m/s Since this change in velocity takes place over 4 seconds, the cars acceleration is

=

Δt

Δv4s20m/s

=5m/s

2 Similarly 30/4 =7.5m/s

3.Let the uniform deceleration of motorcycle =a

Then applying second equation of motion for uniform decelaration:

s=ut+

2

1

at

2

⇒20×15+

2

1

a×225=200 (72kmph=20m/s,s=200m,t=15s)

⇒a=−

225

200

m/s

2

⇒a=−

9

8

m/s

2

(b) Now let velocity of motorcycle when it passes the signal =v

Applying first equation of motion:

v=u+at

v=20−

98

(15)m/s

⇒v=−

9

60 m/s=−

3

20m/s

Answer 2

1. acceleration = final velocity - initial velocity / time
a = 40-20 / 5
a = 20/5
a= 4 m/s square.

2. a= v-u / t
a= 30-0 / 4
a= 7.5 m/s square

3. d= v-u / t
d= 0-70 / 2
d= 35 m/s square ( deceleration value shouldn’t be written in negative as itself it means negative)