Online Test: Laws of Motion | Class 11 Physics

Question 1 of 18

Newton's first law is also called the law of:

gravitation

inertia

momentum

friction

Explanation: The first law describes inertia — the tendency to resist a change in motion.

Question 2 of 18

The SI unit of force is the:

joule

newton

watt

pascal

Explanation: $1\ \text{N}=1\ \text{kg}\cdot\text{m/s}^2$.

Question 3 of 18

Newton's second law in momentum form is:

$\vec{F}=m\vec{v}$

$\vec{F}=\frac{d\vec{p}}{dt}$

$\vec{F}=\vec{p}\,t$

$\vec{F}=\frac{\vec{p}}{t^2}$

Explanation: Force is the rate of change of momentum, $\vec{F}=\frac{d\vec{p}}{dt}$.

Question 4 of 18

A force of 24 N on a 6 kg mass produces an acceleration of:

$2\ \text{m/s}^2$

$4\ \text{m/s}^2$

$6\ \text{m/s}^2$

$18\ \text{m/s}^2$

Explanation: $a=\frac{F}{m}=\frac{24}{6}=4\ \text{m/s}^2$.

Question 5 of 18

Action and reaction forces are equal and opposite but act on:

the same body

different bodies

no body

the heavier body only

Explanation: They act on different bodies, so they never cancel.

Question 6 of 18

A person's apparent weight is zero when the lift is:

accelerating up

moving at constant speed

in free fall

at rest

Explanation: In free fall $a=g$, so $N=m(g-a)=0$.

Question 7 of 18

The SI unit of linear momentum is:

$\text{N}$

$\text{kg}\cdot\text{m/s}$

$\text{kg}\cdot\text{m/s}^2$

$\text{J}$

Explanation: $p=mv$ has units $\text{kg}\cdot\text{m/s}$.

Question 8 of 18

Impulse is equal to the:

change in velocity

change in momentum

change in mass

change in force

Explanation: $\vec{J}=\vec{F}\Delta t=\Delta\vec{p}$.

Question 9 of 18

A 2 kg ball moving at 10 m/s has momentum:

$5\ \text{kg}\cdot\text{m/s}$

$12\ \text{kg}\cdot\text{m/s}$

$20\ \text{kg}\cdot\text{m/s}$

$100\ \text{kg}\cdot\text{m/s}$

Explanation: $p=mv=2\times10=20\ \text{kg}\cdot\text{m/s}$.

Question 10 of 18

The recoil of a gun is explained by:

Newton's first law

conservation of momentum

conservation of energy

friction

Explanation: Total momentum (initially zero) is conserved when the bullet is fired.

Question 11 of 18

A force of 30 N acts for 0.5 s. The impulse is:

$15\ \text{N}\cdot\text{s}$

$60\ \text{N}\cdot\text{s}$

$30\ \text{N}\cdot\text{s}$

$0.5\ \text{N}\cdot\text{s}$

Explanation: $J=F\Delta t=30\times0.5=15\ \text{N}\cdot\text{s}$.

Question 12 of 18

Static friction is:

always equal to $\mu_s N$

self-adjusting up to $\mu_s N$

greater than $\mu_s N$

independent of $N$

Explanation: $f_s\le\mu_s N$; it adjusts to match the applied force up to the limit.

Question 13 of 18

Kinetic friction is given by:

$f_k=\mu_k N$

$f_k=\mu_s N$

$f_k=\frac{N}{\mu_k}$

$f_k=\mu_k N^2$

Explanation: Kinetic friction is $f_k=\mu_k N$.

Question 14 of 18

On an inclined plane of angle $\theta$, the normal reaction equals:

$mg$

$mg\sin\theta$

$mg\cos\theta$

$mg\tan\theta$

Explanation: The component of weight perpendicular to the incline is $mg\cos\theta$.

Question 15 of 18

The angle of repose $\theta$ satisfies:

$\sin\theta=\mu_s$

$\cos\theta=\mu_s$

$\tan\theta=\mu_s$

$\theta=\mu_s$

Explanation: At the angle of repose $\tan\theta=\mu_s$.

Question 16 of 18

The centripetal force needed for circular motion is:

$\frac{mv}{r}$

$\frac{mv^2}{r}$

$\frac{mr}{v^2}$

$mvr$

Explanation: $F=\frac{mv^2}{r}$, directed toward the centre.

Question 17 of 18

For ideal banking of a road, the banking angle satisfies:

$\tan\theta=\frac{rg}{v^2}$

$\tan\theta=\frac{v^2}{rg}$

$\sin\theta=\frac{v^2}{rg}$

$\tan\theta=v^2 rg$

Explanation: $\tan\theta=\frac{v^2}{rg}$ for the ideal banking speed.

Question 18 of 18

A car turns a curve of radius 20 m at 10 m/s; the centripetal acceleration is:

$2\ \text{m/s}^2$

$5\ \text{m/s}^2$

$10\ \text{m/s}^2$

$50\ \text{m/s}^2$

Explanation: $a_c=\frac{v^2}{r}=\frac{100}{20}=5\ \text{m/s}^2$.

Online Test — Laws of Motion