Question:
Two objects having their masses in ratio 3:5 are acted upon by two forces each on one object. The forces are in the ration of 5:3. Find the ratio in their accelerations.
Answer:
Since masses are in ratio 3:5.
Let the mass of the objects be 3x and 5x.
Let F1 and F2are the two forces with a1 and a2 accelerations.
∴ F1 = m1a1 = 3xa1
and F2 = m2a2 = 5xa2
Since F1:F2 = 5:3, we have
3xa1:5xa2 :: 5:3
⇒ a1:a2 = 5×5:3×3
⇒ a1:a2 = 25:9
Force and Laws of Motion
Q 1.
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 2.
When a carpet is beaten with a stick, dust comes out of it. Explain.
Q 4.
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 5.
State Newton’s three laws of motion.
Q 6.
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 0.2m s-2. With what force does each person push the motorcar?
(Assume that all persons push the motorcar with the same muscular effort.)
Q 7.
Why do we tend to fall outwards when a car takes a steep turn?
Q 8.
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 9.
Justify Newton's first law gives notion (or definition) about force.
Q 10.
Why is it advised to tie any luggage kept on the roof of a bus with a rope?
Q 11.
Force can change the shape and size of an object. Give an example.
Q 12.
When a force acts on a body, what are the two essential effects it can produce?
Q 13.
What do you mean by an imapct force?
Q 15.
What is one newton force ?
Q 16.
Derive the relation F = ma,where the symbols have their usual meanings.
Q 17.
What are balanced and unbalanced forces?
Q 18.
While catching a fast moving ball, fielder gradually pulls his hand backwards. Give reasons.
Q 19.
State Law of conservation of momentum.
Q 20.
Fill in the blanks :
When a hanging carpet is beaten with stick, the dust particles start coming out of it. It is due to ______________.
Q 21.
What are unbalanced forces?
Q 22.
What is the momentum of a man of mass 75 kg when he walks with a velocity of 2 m/s ?
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.
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 25.
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 26.
What is the SI unit of force ?
Q 27.
Is momentum a scalar or vector ?
Q 28.
Define momentum of a body.
Q 29.
An unloaded truck weighing 2000 kg has a maximum acceleration of 0.4
.What is the maximum acceleration, when it carries a load of 2000 kg ?
Q 30.
Explain what is meant by momentum of a body.Is it a scalar or a vector ? What are its units ?
Q 31.
Establish relation between inertia and mass.
Q 32.
Why does a gun recoil on firing ? Obtain an expression for recoil velocity of gun.
Q 33.
State Newton’s first law of motion. Hence define force and inertia.
Q 34.
State Newton’s second law of motion and establish that F = ma where symbols have their usual meanings.
Q 35.
Give atleast four applications of Newton’s second law of motion.
Q 36.
State and explain Newton’s third law of motion.How will you prove it experimentally ?
Q 37.
Explain briefly any three applications of Newton’s third law of motion.
Q 38.
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 39.
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-rupee coin and a one-rupee coin?
Q 40.
State Newton's First Law of motion.
Q 41.
Explain why some of the leaves may get detached from a tree if we vigorously shake its branch.
Q 42.
Why do you fall in the forward direction when a moving bus brakes to a stop and fall backwards when it accelerates from rest?
Q 43.
Is force required to keep a moving object in motion (yes/no)?
Q 45.
Which is having higher value of momentum ? A bullet of mass 10 g moving with a velocity of 400 m/s or a cricket ball of mass 400 g thrown with the speed of 90 km/hr.
Q 46.
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 47.
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.
Q 48.
Which of the following graph represents unbalanced force.
Q 49.
Define 1N (Newton).
Q 50.
What is the unit of force in c.g.s system?