## Work power and Energy - Basic Level

Dynamics is the branch of physics developed in classical mechanics concerned with the study of forces and their effects on motion. Isaac Newton was the first to formulate the fundamental physical laws that govern dynamics in classical non-relativistic physics, especially his second law of motion. .

Q1. A labour throws 12 bricks per minute from the ground so as to just reach the roof 3.3 metres high. If each brick weights 3.75 kg, the horse power at which he is working, is
•  0.0325
•  0.325
•  3.25
•  None of these
Solution
horse power at which he is working, is 0.0325

Q2.A weight of 10 metric tons is dragged in half an hour through a distance of 110 metre up a rough inclined plane inclined at an angle of 30 to the horizon, the coefficient of friction being 1/√3. The horse power (nearly) of the engine by which this work will be done is
•  6
•  8
•  10
•  20
Solution
he horse power (nearly) of the engine by which this work will be done is 8

Q3.  A body is 3 kg is projected upwards with such a velocity that it can reach the height 196 metres only. The kinetic energy of the body at the time of projection is
•  5000 Joule
•  5762.4 Joule
•  6000 Joule
•  None of these
Solution
The kinetic energy of the body at the time of projection is 5762.4 Joule

Q4. A bullet of 125 grams strikes a target with a velocity of 400 metres per second and is embedded in it. If the target weighs 10 kg and is free to move, then the velocity of the target after impact is
•  400/81 m/sec
•  400 m/sec
•  300 m/sec
•  None of these
Solution
The kinetic energy of the body at the time of projection is 400/81 m/sec

Q5.A bullet is shot with a velocity of 600 m/sec into a target weighing 12 kg and is free to move with a velocity 1.5 m/sec after impact. Then the percentage loss of kinetic energy in the impact is
•  79.75 %
•  89.75 %
•  99.75 %
•  None of these
Solution
Then the percentage loss of kinetic energy in the impact is 99.75 %

Q6. A 15 kg block is moving on ice with a speed of 5 metre per second when a 10 kg block is dropped onto it vertically. The two together move with a velocity which in metre per second is
•  3
•  √15
• 5
•  None of these
Solution
The two together move with a velocity which in metre per second is 3

Q7.A ball weighing 0.01 kg hits a hard surface vertically with a speed of 5 m/sec and rebounds with the same speed. The ball reamins in contact with the surface for 0.01 sec. The average force exerted by the surface on the ball (in Newton) is
•  0.1
•  1.0
•  5.0
•  10.0
Solution
The average force exerted by the surface on the ball (in Newton) is 10.0

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