Question

A block of mass 3 kg is accelerated from rest to 30 m/s in 2 s. The average force on the block is

Answer 1

Mass of the car m=1000 kg
Initial velocity of car v
1
​
=0
Final velocity of car v
2
​
=100km/h=100×
18
5
​
m/s=27.78m/s
Average power of car=change in kinetic energy per unit time=
t
2
1
​
mv
2
​

2
−
2
1
​
mv
1
​

2

​
,since v
1
​
=0
So,average power of car=
t
2
1
​
mv
2
​

2

​

=
5
2
1
​
×1000×27.78
2

​

=7.71×10
4
W

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Answer 2

The average force on the block is 45 N

Explanation:

Given:

Mass of the block  m = 3 kg

Initial velocity u = 0

Final velocity v = 30 m/s

Time interval t = 2 seconds

To find out:

The average force on the block

Solution:

If the acceleration of the block is a then

Using the first equation of motion

$v=u+at$

$30=0+a\times 2$

$\implies a=\frac{30}{2}$

$\implies a=15$ m/s²

Therefore, the force acting on the block

Using Newton's second law

$F=ma$

$\implies F=3\times 15$ kg × m/s²

$\implies F=45$ N

Hope this answer is helpful.

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