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# A Constant Force Acting on a Body of Mass 3.0 Kg Changes Its Speed from 2.0 M S–1 to 3.5 M S–1 in 25 S. the Direction of the Motion of the Body Remains Unchanged. What is the Magnitude and Direction of the Force - CBSE (Science) Class 11 - Physics

ConceptNewton's Third Law of Motion

#### Question

A constant force acting on a body of mass 3.0 kg changes its speed from 2.0 m s–1 to 3.5 m s–1 in 25 s. The direction of the motion of the body remains unchanged. What is the magnitude and direction of the force?

#### Solution 1

0.18 N; in the direction of motion of the body

Mass of the body, m = 3 kg

Initial speed of the body, u = 2 m/s

Final speed of the body, v = 3.5 m/s

Time, t = 25 s

Using the first equation of motion, the acceleration (a) produced in the body can be calculated as:

v = u + at

:. a = (v -u)/t

= (3.5 - 2)/25 = 1.5/25 = 0.06 "m/s"^2

As per Newton’s second law of motion, force is given as:

F = ma

= 3 × 0.06 = 0.18 N

Since the application of force does not change the direction of the body, the net force acting on the body is in the direction of its motion.

#### Solution 2

Here  m =  3.0 kg, u = 2.0 "ms"^(-1)

v = 3.5 ms^(-1), t = 25 s

As F = ma

or F = m((v-u)/t)        [:. a = (v-u)/t]

=> F = (3.0(3.5 - 2.0))/25  0.18 N

The force is along the direction of motion.

Is there an error in this question or solution?

#### APPEARS IN

Solution A Constant Force Acting on a Body of Mass 3.0 Kg Changes Its Speed from 2.0 M S–1 to 3.5 M S–1 in 25 S. the Direction of the Motion of the Body Remains Unchanged. What is the Magnitude and Direction of the Force Concept: Newton's Third Law of Motion.
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