b) A dog runs 100 m in 20 seconds. He then comes back half the distance in 10 seconds and stops. What is the dog's average velocity? c) A body of mass 1 kg is kept at rest. A constant force of 6 N starts acting on it. Find the time taken by the body to move through a distance of 12 m. d) Draw velocity-time graphs to represent (i) an object travelling with uniform velocity. (ii) an object travelling with uniform acceleration....
Answers
Answer:
We are given a body whose mass is given as
m=1kg
This body is kept at rest so its initial velocity is given as
u=0m/s
A constant force is acting on this body whose magnitude is given as
F=6N
Now from Newton’s second law of motion we can find out the acceleration of the given mass. This can be done in the following way.
F=maa=
F
m
Inserting the value of force and mass, we get
a=
6
1
=6m/s2
We want to move this body using the above force through a distance which is given as
S=12m
So we can make use of the second equation of motion in order to obtain the time taken to move the mass through the above distance.
S=ut+
1
2
at2
Inserting the known values, we get
12=0+
1
2
×6×t2t2=
12
3
=4t=2s
This is the required value of the time. Therefore, it takes 2 seconds for the body to move through a distance of 12 m under the action of a constant force of 6N.
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Explanation:
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A)Given , Mass of object, m=10 kg
Velocity of object, v=20ms
−1
Initial Kinetic energy, K
1 = 2/1
×10×20/2
=2000 J
Now, Final mass, m
2
=20 kg
Final Velocity, v
2
=10m/s
Final Kinetic energy, K
2 = 2/1
×20×10/2
=1000 J
Required Ratio = K /2
K /1= 1000/2000
=2:1
D) this is the velocity-time graph for uniform motion.
slope of this graph=velocity × time=acceleration.
