Question:
If the set of forces acting on an object are balanced, then object
(a) must be at rest.
(b) must be moving
(c) must not be accelerating.
(d) none of these.
Answer:
(c) must not be accelerating. If the forces are balanced, the object will remain in its present state i.e. if it is moving, it will keep on moving with uniform speed. If it is at rest, it will remain at rest.
Force and Laws of Motion
Q 1.
Can balanced forces move a body at rest ?
Q 2.
A stone of 1 kg is thrown with a velocity if 20
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 ?
Q 3.
State Newton's First Law of motion.
Q 4.
A bullet of mass 10 g travelling horizontally with a velocity of 150 m/s 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.
Q 5.
Fill in the blanks :
It is dangerous to jump out of a moving bus because due to _________ one falls forward.
Q 6.
A man pushes a box of mass 50 kg with a force of 80 N.What will be the acceleration of the box ? What would be the acceleration if the mass were halved ?
Q 7.
Two objects of masses 100 g and 200 g are moving along the same line in the same direction with velocities of 2 m/s and 1 m/s,respectively.They collide and after the collision, the first object moves at a velocity of 1.67 m/s in the same direction.Determine the velocity of the second object
Q 8.
A hockey ball of mass 200 g travelling at 10 m/s is struck by a hockey stick so as to return it along its original path with a velocity of 5 m/s.Calculate the change in momentum of the hockey ball by the force applied by the hockey stick.
Q 9.
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 24
on a mass
.What acceleration would the same force provide if both the masses are tied together ?
Q 10.
Do action-reaction forces act on the same body ?
Q 12.
Name the three types of inertia.
Q 13.
Define momentum of a body.
Q 14.
What would be the force required to produce an acceleration of 2
in a body of mass 12 kg ? What would be the acceleration if the force were doubled ?
Q 15.
A body of mass 1 kg is kept at rest.A constant force of 6-0 N starts acting on it.Find the time taken by the body to move through a distance of 12 m.
Q 16.
A hammer of mass 500 g,moving at 50 m/s,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 ?
Q 17.
A person in a bus tends to fall backwards, when it starts suddenly ?
Q 18.
What is force ? What is inertia ? How is inertia measured ?
Q 19.
Derive the relation F = ma,where the symbols have their usual meanings.
Q 20.
Why is it advised to tie any luggage kept on the roof of a bus with a rope?
Q 21.
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 metric tonnes. (Hint: 1 metric tonne = 1000 kg.)
Q 22.
Which would require a greater force : accelerating a 2 kg mass at 5
or a 4 kg mass at 2
?
Q 23.
A force of 5 N gives a mass
an acceleration of 10
,and a mass
,an acceleration of 20
.What acceleration would it give if both the masses were tied together ?
Q 24.
What are balanced forces ?
Q 25.
In the above question,which body undergoes greater change in momentum ?
Q 26.
Show that kg-
and N-s represent the same quantity.Which is that quantity ?
Q 27.
Honey and Sunny are two friends.Both are financially well off.Honey is fond of driving an SUV while Sunny enjoys driving Tata Nano.Honey explains to Sunny the risks of driving a light vehicle and Sunny explains to Honey the cost factor.
Read the above passage and answer the following questions :
(i) With whom do you agree,with Honey or with Sunny?
(ii) Explain, why?
(iii) Which values of life do you learn from this discussion?
Q 28.
If the set of forces acting on an object are balanced, then object
(a) must be at rest.
(b) must be moving
(c) must not be accelerating.
(d) none of these.
Q 29.
Define 1N (Newton).
Q 30.
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?
Q 31.
Fill in the blanks :
The ______ of an object is a measure of its inertia.
Q 32.
Fill in the blanks :
________ is the tendency of an object to resist a change in motion.
Q 33.
Define 1 Newton force.
Q 34.
What are unbalanced forces ?
Q 35.
Discuss briefly Galileo's ideas about motion.
Q 36.
State Newton’s three laws of motion.
Q 37.
State Newton’s first law of motion. Hence define force and inertia.
Q 38.
State and explain Newton’s third law of motion.How will you prove it experimentally ?
Q 39.
Explain briefly any three applications of Newton’s third law of motion.
Q 40.
When two objects act on each other, does action-reaction force pair cancel out each other?
Q 41.
Fill in the blanks :
An umbrella protects us from rain it is based on the property of _____________.
Q 42.
Fill in the blanks :
When a car enters a curved path, the person sitting in it is thrown outwards. This is because of the property of ______________.
Q 43.
Fill in the blanks :
________ is a measure of intertia.
Q 44.
Force can change the shape and size of an object. Give an example.
Q 45.
When a force acting on a body has equal and opposite reaction, then why should the body move at all?
Q 46.
A bullet of mass 50 g is fired from a gun of mass 6 kg with a velocity of 400 m/s.Calculate the recoil velocity of the gun.
Q 47.
A boy of mass 60 kg running at 3 m/s jumps on to a trolley of mass 140 kg moving with a velocity of 1.5 m/s in the same direction.What is their common velocity ?
Q 48.
Two hockey players of opposite teams,while trying to.hit a hockey ball on the ground collide and immediately become entangled.One has a mass of 60 kg,and was moving with a velocity 5.0 m/s,while the other has a mass of 55 kg and was moving faster with a velocity of 6.0 m/s towards the first player,In which direction and with what velocity will they move after they become entangled ? Assume that the frictional force acting between the feet of the two players and ground is negligible.
Q 49.
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
?
Q 50.
A bullet of mass 10 g travelling horizontally with a velocity of 150
strikes a 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.
