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Conceptual questions

1. Why we are hurt less when we jump on a muddy floor in comparison to a hard floor?
2. Why are shockers used in cars, scooters and motorcycles
3.Why is it necessary to bend knees while jumping from greater height?

4.A cricket player lowers his hands to catch the ball safely.Explain why?
NUMERICALS

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1. A car of mass 1000 kg is moving with a velocity of 10 ms and is acted upon by a
forward force of 1000 N due to engine and retarding force of 500 N due to friction. What
will be its velocity after 10 seconds?

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2.A bullet of mass 0.04 kg moving with a speed of 90 ms enters a heavy wooden block
and is stopped after a distance of 60 cm What is the average resistive force exerted by
the block on the bullet?

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3. A scooterist moving with a speed of 36 kmh sees a child standing in the middle of
the road. He applies the brakes and brings the scooter to rest in 5 s just in time to save
child. Calculate the average retarding force on the vehicle, if mass of the vehicle and
driver is 300 kg.
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4.A force of 5 N gives a mass an acceleration of 8 ms and a mass m 2 an acceleration
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of 24 ms . What acceleration would it give if both the masses are tied together?
5. A truck starts from rest and rolls down a hill with constant acceleration. It travels a
distance of 400 m in 20 s. Calculate the acceleration and the force acting on it if its
mass is 7 metric tonnes.

6.A force acts for 10 s on a body of mass 10 kg after which the force ceases and the
body describes 50 m in the next 5 s. Find the magnitude of the force.

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7.A ship of mass 3 × 10 kg and initially at rest can be pulled through a distance of 3 m
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by means of a force of 5 × 10 N. The water resistance is negligible. Find the speed
attained by the ship.
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8. A cricket ball of mass 150 g moving with a velocity of 15 ms is brought to rest by a
player in 0.05 s. Calculate the impulse and the average force exerted by the player.

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9. A hammer weighing 1 kg moving with the speed of 10 ms strikes the head of a nail
driving it 10 cm into a wall. Neglecting the mass of the nail, calculate (i) the acceleration
during impact (ii) the time interval of the impact and (iii) the impulse.

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10. A machine gun fires a bullet of mass 40 g with a speed of 1200 ms . The person
holding the gun can exert a maximum force of 144 N on it. What is the number of bullets
that can be fired from the gun per second?

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11.The initial speed of a body of mass 2.0 kg is 5.0 ms . A force acts for 4 s in the
direction of motion of the body. The force-time graph is shown in Fig. Calculate the
impulse of the force and the final speed of the body