Question

A certain force exerted for 1.2 seconds raises the speed of an object from 1.8m/s to 4.2m/s. Later the same force is applied for 2 seconds. How much does the velocity change in 2 seconds?

Answer 1

Initial velocity (u) = 1.8 m/s.
Final velocity (v) = 4.2 m/s
Time (t) = 1.2 seconds
First calculate acceleration

a = (v-u)/t = (4.2 - 1.8)/1.2= 2 m/s²

As the same force acts for the next two seconds the acceleration produced will be the same.
The final velocity in the first case will now become the initial velocity.
We have to calculate the final velocity at end of 2 seconds.
Acceleration (a) = 2 m/s²
Intial velocity (u) = 4.2 m/s,
t = 2 s
Final velocity (v) = ?
[First equation of motion]
v = u + at [First equation of motion]
= 4.2 + 2 x2
= 4.2 + 4
= 8.2 m/s
Change in velocity in two seconds
= 8.2 - 4.2 = 4 m/s

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