Question

A force acts for 8 s on a body of mass 5 kg at rest, on
a smooth horizontal surface. The force then stops
acting and the body describes 80 m in next 5 s. The
force acting on body is​

Answer 1

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Force acted on body = 10N.

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Since the body was initially at rest before application of force thus we can say

Initial velocity of body = 0m/s.

Now,Mass of body = 5kg

Time for which force acted = 8s

Now after 8 secs of application the force stopped acting and it's given that the body acquired a constant velocity and moved 80m in next 5s.

So in case two ( after removal of force)

Distance travelled = 80m

Time taken = 5s.

Thus we can say after removal of force the body traveled with a velocity of

$v = d \div t$

$v = 80 \div 5$

v = 16m/s

Thus we get final velocity of body is 16m/s.

Now for a body acceleration is --------->

$v - u \div t$

$16 - 0 \div 2$

$16 \div 2 = 8m \div {s}^{2}$

Now acceleration of body was 8m/ s^2.

Now for a body force is product of mass and acceleration.

Thus force acting on this body is

$f = 5 \times 2$

$f = 10n$

Thus force acting on body was 10N.

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Answer 2

Topic

Mechanics

Given

A force acts for 8 seconds on a body of mass 5 kg at rest kept on a smooth horizontal surface.

The force then stops acting and the body describes 80 metres in next 5 seconds.

To Find

The force acting.

Formula to be Used

Change in momentum is equal to Impulse of the body.

Ft = m∆v

where

• F = Force on the body
• t = Time for which force is applied
• m = Mass of given body
• ∆v = Change in Velocity

∆v = Final Velocity - Initial Velocity

Solving

Calculating the final speed of block after removal of applied Force.

Velocity = Displacement / Time

Velocity = 80 m / 5 seconds

Velocity = 16 m/s

Initial Velocity of the block is zero.

So,

∆v = 16 - 0

∆v = 16 m/s

Force was applied for 8 seconds.

So, t = 8 seconds

m = 5 kg

Now, applying the formula,

Ft = m∆v

F × 8 = 5 × 16

F × 8 = 80

F = 10 N

Answer

The force acting on the body is 10N.

Learn More :-

Impulse

It is a term which describes the effect of a Force acting over a time interval.

Its SI Unit is N-s.