To prove!!!2

The instantaneous velocity of a 2kg body is given by-

v=18t + 3 where v=instantaneous velocity(in m/s) and t=time(in seconds)

Find the work done by the force from t=0sec to t=5sec.(in Joules)


My inspiration Aniket Sanghi


The answer is 8640.

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3 solutions

Steven Chase
Mar 6, 2018

Power:

P = F v = m a v = 2 ( 18 ) ( 18 t + 3 ) = 36 ( 18 t + 3 ) P = F \, v = m \, a \, v \\ = 2(18)(18 t + 3) \\ = 36(18 t + 3)

Energy:

E = 0 5 P d t = 36 0 5 ( 18 t + 3 ) d t = 36 ( 9 ( 5 2 ) + 3 ( 5 ) ) = 8640 E = \int_0^5 P \, dt \\ = 36 \int_0^5 (18 t + 3) \, dt \\ = 36 \, (9(5^2) + 3(5)) \\ = 8640

Sir, how to make Integration sign bigger?

Aryan Sanghi - 3 years, 1 month ago

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You can make text and symbols bigger by using \large{} or \Large{}, and putting the desired symbol or text inside the brackets

Steven Chase - 3 years, 1 month ago

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Oh, thanks

Aryan Sanghi - 3 years, 1 month ago

Nice and concise. I knew that the force is not variable, so I did not use any calculus, because I did not incorporate power into my solution. Good solution.

Krishna Karthik - 2 years, 6 months ago
Krishna Karthik
Nov 15, 2018

Since the force is constant, the definition of work as an integral is not needed. The acceleration is found by

d v d t \Large\frac{dv}{dt} , which in this case is 18m/s 2 ^2

Newton's second law:

F = m a = 2 18 = 36 N \Large F=ma = 2*18=36N

Work:

W = F d = 36 d \Large W=Fd=36d

displacement is found by integrating velocity:

18 t + 3 \Large\int 18t+3 = 3 t + 9 t 2 \Large3t+9t^2

substituting t=5;

d = 240 \Large d=240

Therefore, the work done is 36 d = 240 36 = 8640 J \Large36d=240*36=8640J

Aryan Sanghi
Mar 6, 2018

Displacement:

s = 0 5 v d t = 0 5 ( 18 t + 3 ) d t = 240 s=\int_0^5 v\, dt\\=\int_0^5 (18t+3)\, dt\\=240


Acceleration:

a= d v d t \frac{dv}{dt}

= d d t \frac{d}{dt} (18t+3)

=18m/s 2 ^2


Energy

E=Fs

=mas

=2×18×240

=8640


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