Physics

Force and Laws of Motion

Question:

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 before the collision during which they stick together. What will be the velocity of the combined object after collision?

Answer:

Given
mass of the first object (m1) = 1.5 kg
velocity of the first object (u1) before collision = 2.5 m/s

mass of the second object (m2) = 1.5kg
velocity of the second object (u2) before collision = -2.5 m/s
The negative sign indicates the second object moves in direction opposite to the first one.

mass of the combined objects after collision (m3) =  m1+ m2= 3.0 kg
velocity of the combined objects after collision (v3) =?

Being an isolated system, total momentum is conserved i.e.
(m1u1) + (m2u2) =  (m3v3)
⇒ (1.5 × 2.5) + (1.5 × -2.5) = 3.0 × v3
⇒  0 = 3.0 × v3
⇒ v3 = 0 m/s

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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 8 m s-2 on a massm1 and an acceleration of 24m s-2 on a mass m2.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 3.

Define intertia.

Q 4.

A stone of 1 kg is thrown with a velocity if 20 ms-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 ?

Q 5.

State Newton’s three laws of motion.

Q 6.

Why do we tend to fall outwards when a car takes a steep turn?

Q 7.

What would be the force required to produce an acceleration of 2 m/s2 in a body of mass 12 kg ? What would be the acceleration if the force were doubled ?

Q 8.

Justify Newton's first law gives notion (or definition) about force.

Q 9.

Why is it advised to tie any luggage kept on the roof of a bus with a rope?

Q 10.

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 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.

Define force.

Q 14.

What is one newton force ?

Q 15.

Derive the relation F = ma,where the symbols have their usual meanings.

Q 16.

While catching a fast moving ball, fielder gradually pulls his hand backwards. Give reasons.

Q 17.

State Law of conservation of momentum.

Q 18.

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 19.

What are unbalanced forces?

Q 20.

What do you mean by an imapct force?

Q 21.

A force of 5 N gives a mass m1 an acceleration of 10 m/s2,and a mass m2,an acceleration of 20 m/s2.What acceleration would it give if both the masses were tied together ?

Q 22.

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 23.

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 24.

What is the SI unit of force ?

Q 25.

Is momentum a scalar or vector ?

Q 26.

Define momentum of a body.

Q 27.

An unloaded truck weighing 2000 kg has a maximum acceleration of 0.4 m/s2.What is the maximum acceleration, when it carries a load of 2000 kg ?

Q 28.

Explain what is meant by momentum of a body.Is it a scalar or a vector ? What are its units ?

Q 29.

Establish relation between inertia and mass.

Q 30.

Why does a gun recoil on firing ? Obtain an expression for recoil velocity of gun.

Q 31.

State Newton’s first law of motion. Hence define force and inertia.

Q 32.

State Newton’s second law of motion and establish that F = ma where symbols have their usual meanings.

Q 33.

Give atleast four applications of Newton’s second law of motion.

Q 34.

State and explain Newton’s third law of motion.How will you prove it experimentally ?

Q 35.

Explain briefly any three applications of Newton’s third law of motion.

Q 36.

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 37.

State Newton's First Law of motion.

Q 38.

Explain why some of the leaves may get detached from a tree if we vigorously shake its branch.

Q 39.

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 40.

Is force required to keep a moving object in motion (yes/no)?

Q 41.

Define momentum.

Q 42.

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 43.

What are balanced and unbalanced forces?

Q 44.

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 45.

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 46.

Which of the following graph represents unbalanced force.

Q 47.

Define 1N (Newton).

Q 48.

What is the unit of force in c.g.s system?

Q 49.

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 50.

How Newton's Second law of motion is different from First law?