Physics Test

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Physics Test - 16

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Weekly Quiz Competition

Question 1
1 / -0

The statement 'Acceleration is zero if and only if the net force is zero' is valid in.........

A
Non-inertial frames

B
Inertial frames

C
Both in an inertial frames and non-inertial frames

D
Neither inertial frames nor non-inertial frames

Solution

According to Newton's second law, force is the rate of change of momentum in an inertial frame. Thus, if the net external force acting on the body is 0, the net acceleration will also be 0.
Hence, the correct option is B.
Question 2
1 / -0

A monkey pulls the midpoint of a 10cm long light inextensible string connecting two identical objects A and B of masses 0.3kg lying on smooth table continuously along the perpendicular bisector of line joining the masses. The masses are found to approach each other at a relative acceleration of 5ms−2 when they are 6cm apart. The constant force applied by monkey is:

A
4N

B
2 N

C
3 N

D
None of these

Solution

With reference to the diagram Note: The acceleration of both objects are symmetrical due to the symmetry of the system. Relative acceleration \(=5 m / s^{2}\) \(\Rightarrow 2 a_{1}=5\)
\(\Rightarrow a_{1}=2.5 m / s^{2}\)
According to the free body diagram of left block, \(m a_{1}=T \cos \theta\)
\(\Rightarrow 0.3 \times 2.5=\frac{3 T}{5}\)
\(\Rightarrow T=1.25 N\)
According to free body diagram of the intersection point of force and string, \(F=2 T \sin \theta\)
\(\Rightarrow F=2 \times 1.25 \times\left(\frac{4}{5}\right)\)
\(\Rightarrow F=2 N\)
Hence, the correct option is B.
Question 3
1 / -0

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

Solution

The ball slows to a stop because there is a force on the ball opposing the motion,and this force is the force of friction between the ball and the surface of ground.
Hence, the correct option is C.
Question 4
1 / -0

A car starts from rest and is uniformly accelerated to a speed of 30 m/s in 6s. What is the distance travelled by the car ?

A
5 m

B
30 m

C
90 m

D
180 m

Solution

\(s=u \times t+\frac{1}{2} \times a \times t^{2}\)
\(a=\frac{v-u}{t}\)
where s is Distance travelled. u is initial speed. v is final speed. a is Acceleration.
t is time. Given \(: u=0, v=30 \frac{m}{s}, t=6 s e c\)
\(a=\frac{30}{6} \quad\) using equ.
\(a=5 \frac{m}{s^{2}}\)
\(s=0+\frac{1}{2} \times 5 \times 6^{2} \quad\) using equ.
\(s=90 m\)
Hence, the correct option is C.
Question 5
1 / -0

The square of resultant of two equal forces is three times their product. Angle between the forces is:

A
π

B
π/2

C
π/4

D
π/3

Solution

Let \(\phi\) be the angle between the forces. Thus, \(F_{n e t}^{2}=F_{1}^{2}+F_{2}^{2}+2 F_{1} F_{2} \cos \phi=3 F_{1} F_{2}\)
\(\Longrightarrow F^{2}+F^{2}+2 F^{2} \cos \phi=3 F^{2}\)
\(\Longrightarrow \cos \phi=\frac{1}{2}\)
\(\Longrightarrow \phi=\frac{\pi}{3}\)
Hence, the correct option is D.
Question 6
1 / -0

Which will have least inertia?

A
A football

B
A needle

C
A thread

D
A refrigerator

Solution

The object having the greatest mass has the greatest inertia and vice-versa.
As the the thread is the lightest object among the given options, thus thread will have the least inertia.
Hence, the correct option is C.
Question 7
1 / -0

A particle starts sliding down a frictionless inclined plane. If S_n is the distance traveled by it from time t= n-1 sec to t= n sec, the ratio S_n/S_n+1 is :

A
(2n−1)/(2n+1)

B
(2n+1)/2n

C
2n/(2n+1)

D
(2n+1)/(2n−1)

Solution

Distance travelled by the particle in nth second is given by
\(S_{n t h}=\frac{(2 n-1) a}{2}\)
Where \(n\) is the nth second and \(a\) is the acceleration of the particle
\(S_{n+1 t h}=\frac{(2(n+1)-1) a}{2}\)
\(S_{n t h} / S_{n+1 t h}=\frac{(2 n-1)}{(2(n+1)-1)}\)
Ratio \(=\frac{(2 n-1)}{(2 n+1)}\)
Hence, the correct option is A.
Question 8
1 / -0

Larger the slope of a velocity-time graph.

A
lower is the acceleration

B
higher is the acceleration

C
lower the displacement

D
higher the displacement

Solution

If the acceleration is negative, then the velocity-time graph is a downward sloping line (i.e., the slope is negative). If the acceleration is great, then the line slopes up steeply (i.e., the slope is great). This principle can be extended to any motion conceivable
Hence, the correct option is B.
Question 9
1 / -0

As the train starts moving; a man sitting inside leans backwards because of :

A
Inertia of rest

B
Inertia of motion

C
Moment of inertia

D
Conservation of mass

Solution

From Newton's first law of motion, an object which is initially at rest will continue to do so unless an external force acts on it. Hence, when the train starts moving, the man is still at rest and hence appears to move backwards with respect to the train. This is called as Inertia of rest.
Hence, the correct option is A.
Question 10
1 / -0

A bullet of mass mm is fired from the gun, the acceleration of the bullet is:

A
greater than the acceleration of the gun

B
equal to the acceleration of the gun

C
equal but opposite to the acceleration of the gun

D
directly proportional to the mass of the bullet

Solution

Action reaction pair is formed when bullet is fired. Equal and opposite forces act on the bullet and the gun.
Now we know that the acceleration caused due to a force=a=F/m
Thus for same force, the smaller mass object has greater acceleration. Thus the acceleration of the bullet is greater than that of gun.
Hence, the correct option is A.

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Physics Test - 16

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Physics Test - 16

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Question 1

Non-inertial frames

Inertial frames

Both in an inertial frames and non-inertial frames

Neither inertial frames nor non-inertial frames

Solution

Question 2

4N

2 N

3 N

None of these

Solution

Question 3

the batsman did not hit the ball hard enough

velocity is proportional to the force exerted on the ball

there is a force on the ball opposing the motion

there is no unbalanced force on the ball, so the ball would want to come to rest

Solution

Question 4

5 m

30 m

90 m

180 m

Solution

Question 5

π

π/2

π/4

π/3

Solution

Question 6

A football

A needle

A thread

A refrigerator

Solution

Question 7

(2n−1)/(2n+1)

(2n+1)/2n

2n/(2n+1)

(2n+1)/(2n−1)

Solution

Question 8

lower is the acceleration

higher is the acceleration

lower the displacement

higher the displacement

Solution

Question 9

Inertia of rest

Inertia of motion

Moment of inertia

Conservation of mass

Solution

Question 10

greater than the acceleration of the gun

equal to the acceleration of the gun

equal but opposite to the acceleration of the gun

directly proportional to the mass of the bullet

Solution

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