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An object experiences a net zero external unbalanced force. Is it possible for the object to be travelling with a non-zero velocity? If yes, state the conditions that must be placed on the magnitude and direction of the velocity. If no, provide a reason.
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When a carpet is beaten with a stick, dust comes out of it. Explain.
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Why is it advised to tie any luggage kept on the roof of a bus with a rope?
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A batsman hits a cricket ball which then rolls on a level ground. After covering a short distance, the ball comes to rest. The ball slows to a stop because
(a) the batsman did not hit the ball hard enough.
(b) velocity is proportional to the force exerted on the ball.
(c) there is a force on the ball opposing the motion.
(d) there is no unbalanced force on the ball, so the ball would want to come to rest.
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A truck starts from rest and rolls down a hill with a constant acceleration. It travels a distance of 400 m in 20 s. Find its acceleration. Find the force acting on it if its mass is 7 tonnes
(Hint: 1 tonne = 1000 kg.)
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A stone of 1 kg is thrown with a velocity of 20 m s–1 across the frozen surface of a lake and comes to rest after travelling a distance of 50 m. What is the force of friction between the stone and the ice?
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A 8000 kg engine pulls a train of 5 wagons, each of 2000 kg, along a horizontal track. If the engine exerts a force of 40000 N and the track offers a friction force of 5000 N, then calculate
(a) the net accelerating force;
(b) the acceleration of the train; and
(c) the force of wagon 1 on wagon 2
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An automobile vehicle has a mass of 1500 kg. What must be the force between the vehicle and road if the vehicle is to be stopped with a negative acceleration of 1.7 m s–2?
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What is the momentum of an
object of mass m, moving with a velocity
?
(a)
(b)
(c)
(d)
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Using a horizontal force of 200 N, we intend to move a wooden cabinet across a floor at a constant velocity. What is the friction force that will be exerted on the cabinet?
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Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 m s–1 before the collision during which they stick together. What will be the velocity of the combined object after collision?
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According to the third law of motion when we push on an object, the object pushes back on us with an equal and opposite force. If the object is a massive truck parked along the roadside, it will probably not move. A student justifies this by answering that the two opposite and equal forces cancel each other. Comment on this logic and explain why the truck does not move.
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A hockey ball of mass 200 g travelling at 10 m s–1 is struck by a hockey stick so as to return it along its original path with a velocity at 5 m s–1. Calculate the change of momentum occurred in the motion of the hockey ball by the force applied by the hockey stick.
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A bullet of mass 10 g travelling horizontally with a velocity of 150 m s-1 strikes a stationary wooden block and comes to rest in 0.03 s. Calculate the distance of penetration of the bullet into the block. Also calculate the magnitude of the force exerted by the wooden block on the bullet.
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An object of mass 1 kg travelling in a straight line with a velocity of 10 m s–1 collides with, and sticks to, a stationary wooden block of mass 5 kg. Then they both move off together in the same straight line. Calculate the total momentum just before the impact and just after the impact.
Also, calculate the velocity of the combined object.
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An object of mass 100 kg is accelerated uniformly from a velocity of 5 m s–1 to 8 m s–1 in 6 s. Calculate the initial and final momentum of the object. Also, find the magnitude of the force exerted on the object,
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Akhtar, Kiran and Rahul were riding in a motorcar that was moving with a high velocity on an expressway when an insect hit the windshield and got stuck on the windscreen. Akhtar and Kiran started pondering over the situation. Kiran suggested that the insect suffered a greater change in momentum as compared to the change in momentum of the motorcar (because the change in the velocity of the insect was much more than that of the motorcar). Akhtar said that since the motorcar was moving with a larger velocity, it exerted a larger force on the insect. And as a result the insect died. Rahul while putting an entirely new explanation said that both the motorcar and the insect experienced the same force and a change in their momentum.
Comment on these suggestions.
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How much momentum will a dump-bell of mass 10 kg transfer to the floor if it falls from a height of 80 cm? Take its downward acceleration to be 10 m s-1.
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Which of the following has more inertia:
(a) a rubber ball and a stone of the same size?
(b) a bicycle and a train?
(c) a five-rupees coin and a one-rupee coin?
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In the following example, try to identify the number of times the velocity of the ball changes:
“A football player kicks a football to another player of his team who kicks the football towards the goal. The goalkeeper of the opposite team collects the football and kicks it towards a player this own team”.
Also identify the agent supplying the force in each case.
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Explain why some of the leaves may get detached from a tree if we vigorously shake its branch.
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Why do you fall in the forward direction when a moving bus brakes to a stop and fall backwards when it accelerates from rest?
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If action is always equal to the reaction, explain how a horse can pull a cart.
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Explain, why is it difficult for a fireman to hold a hose, which ejects large amounts of water at a high velocity?
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From a rifle of mass 4 kg, a bullet of mass 50 g is fired with an initial velocity of 35 m s-1. Calculate the initial recoil velocity of the rifle.
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Two objects of masses 100 g and 200 g are moving along the same line and direction with velocities of 2 m s-1 and 1 m s-1 respectively. They collide and after the collision, the first object moves at a velocity of 1.67 m s-1. Determine the velocity of second object.
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The following is the distance-time table of an object in motion :
|
Time (in seconds)
|
Distance (in metres)
|
|
0
|
0
|
|
1
|
1
|
|
2
|
8
|
|
3
|
27
|
|
4
|
64
|
|
5
|
125
|
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6
|
216
|
|
7
|
343
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(a) What conclusion can you draw about the acceleration? Is it constant, increasing, decreasing, or zero?
(b) What do you infer about the forces acting on the object?
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Two persons manage to push a motorcar of mass 1200 kg at a uniform velocity along a level road. The same motorcar can be pushed by three persons to produce an acceleration of 0.2 m s-2. With what force does each person push the motorcar? (Assume that all persons push the motorcar with the same muscular effort.)
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A hammer of mass 500 g, moving at 50 m s-1, strikes a nail. The nail stops the hammer in a very short time of 0.01 s. What is the force of the nail on the hammer?
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A motorcar of mass 1200 kg is moving along a straight line with a uniform velocity of 90 km/h. Its velocity is slowed down to 18 km/h in 4 s by an unbalanced external force. Calculate the acceleration and change in momentum. Also calculate the magnitude of the force require.
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A large truck and a car, both moving with a velocity of magnitude v, have a head-on collision and both of them come to a halt after that. If the collision lasts for 1s:
(a) Which vehicle experiences the greater force of impact?
(b) Which vehicle experiences the greater change in momentum?
(c) Which vehicle experiences the greater acceleration?
(d) Why is the car likely to suffer more damage than the truck?
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question_answer32)
Which of the following statement is not correct for an object moving
along a straight path in accelerated motion?
(a) Its speed keeps changing (b)
Its velocity always changes
(c) It always goes away from the earth (d)
A force is always acting on it
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question_answer33)
According to the third law of motion, action and reaction
(a) always act on the same body (b)
always act on different bodies in opposite directions
(c) have same magnitude and direction (d)
act on either body at normal to each other
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question_answer34)
A goalkeeper in a game of football pulls his hands
backwards after holding the ball shot at the goal. This enables the goalkeeper
to
(a) exert larger force on the ball (b)
reduce the force exerted by the ball on hands
(c) increase the rate of change of momentum (d)
decrease the rate of change of momentum
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question_answer35)
The inertia of an object tends to cause the object
(a) to increase its speed (b)
to decrease its speed
(c) to resist any change in its state of motion (d)
to decelerate due to friction
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question_answer36)
A passenger in a moving train tosses a coin which falls
behind him. It means that motion of the train is
(a) accelerated (b) uniform (c)
retarded (d) along circular tracks
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question_answer37)
An object of mass 2 kg is sliding with a constant velocity
of 
on a frictionless
horizontal table. The force required to keep the object moving with the same
velocity is
(a) 32 N (b) 0 N (c)
2 N (d) 8 N
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question_answer38)
Rocket works on the principle of conservation of
(a) mass (b) energy (c)
momentum (d) velocity
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question_answer39)
A water tanker filled upto 
of its
height is moving with a uniform speed.
On sudden application of the brake, the water in the tank
would
(a) move backward (b) move forward (c)
be unaffected (d) rise upwards
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question_answer40)
There are three solids made up of aluminium, steel and
wood of the same shape and same volume. Which of them would have highest
inertia?
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question_answer41)
Two balls of the same size but of different materials,
rubber and iron, are kept on the smooth floor of a moving train. The brakes are
applied suddenly to stop the train. Will the balls start rolling? If so, in
which direction? Will they move with the same speed? Give reasons for your answer.
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question_answer42)
Two identical bullets are fired one by one by a light
rifle and another by a heavy rifle with the same force, which rifle will hurt
the shoulder more and why?
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question_answer43)
A horse continues to apply a force in order to move the
cart with a constant speed. Explain why?
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question_answer44)
Suppose a ball of mass m is thrown vertically upward with
an initial speed v, its speed decreases continuously till it becomes zero.
Thereafter, the ball begins to fall downward and attain
the speed v again before striking the ground. It implies that the magnitude of
initial and final momentums of the ball are same. Yet, it is not an example of conservation
of momentum. Explain why?
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question_answer45)
Velocity versus time graph of a ball of mass 50 g rolling
on a concrete floor is shown in figure. Calculate the acceleration and
frictional force of the floor on the ball.
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question_answer46)
A truck of mass m is moved under a force F. If the truck
is then loaded with an object equal to the mass of the truck and the driving
force is halved, then how does the acceleration change?
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question_answer47)
Two friends on roller skates are standing 5 m apart facing
each other.
One of them throws a ball of 2 kg towards the other, who
catches it. How will this activity affect the position of the two? Explain your
answer.
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question_answer48)
Water sprinkler used for grass lawn begins to rotate as
soon as the water is supplied. Explain the principle on which it works.
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question_answer49)
Using second law of motion, derive the relation between
force and acceleration. A bullet of 10 g strikes a sand-bag at speed of 
and gets
embedded after travelling 5 cm. Calculate
(i) the resistive force exerted by the sand on the bullet.
(ii) the time taken by the bullet to come to rest.
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question_answer50)
Derive the unit of force using the second law of motion. A
force of 5 N produces an acceleration of 
on a
mass 
and an
acceleration of 
on
a mass 
. What
acceleration would the same provide, if both the masses are tied together?
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question_answer51)
What
is momentum? Write its Sl unit. Interpret force in terms of momentum. Represent
the following graphically
(i) momentum versus velocity when mass is fixed.
(ii) momentum versus mass when velocity is constant.
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