Class 11th

This is a Short Answer type Questions as classified in NCERT Exemplar

Explanation- porcelain objects are wrapped in paper while transporting because they are very fragile can easily break. while we wrapped them in paper to increase the time so the damage to them is as less as possible.

This is a Short Answer type Questions as classified in NCERT Exemplar

Explanation -the frictional force shown on vertical axis and the applied force shown on horizontal axis. The portion OA of graph represents static friction which is a self-adjusting .in this f=F.

Whereas the point B represents force of limiting friction . Cd|OX represents kinetic friction. The force of kinetic friction does not change by applying force.

This is a Short Answer type Questions as classified in NCERT Exemplar

Explantion -  given mass of the body = 2kg

Velocity of the body = 2t? +t²?

Velocity of body at t=2s

V= 2 $*2$ ? +2²? = 4? +4?

Momentum of body =mv = 2 (4? +4? )= 8? +8? kgm/s

Acceleration a= dv/dt

= d/dt (2t? +t²? )= 2? +2t?

At t=2s, a= (2i+2 (2)j)= 2? +4?

Force acting on the body F=ma

=2 (2? +4? )

= 4? +8? N

This is a Short Answer type Questions as classified in NCERT Exemplar

Explanation- when a person driving car suddenly applies brakes the lower comes to rest but the upper part of the body will remain in motion. so if the driver not wearing seat belt will falls forward and his head hit against the steering wheel.

This is a Short Answer type Questions as classified in NCERT Exemplar

Explanation- mass of body =2kg

From the above graph the body at x=0 when t=0 so body at rest.

So impulse is also zero.

From t=0s to t=4s graph becomes straight line which shows body is at uniform velocity

Beyond 4s graph is parallel to time axis, body is at rest

So tan $\theta$ =3/4

Impulse at t=4s= change in momentum= mv-mu

 =m (v-u)

 = 2 (0-3/4)= -3/2kgm/s

This is a Short Answer type Questions as classified in NCERT Exemplar

Explanation – w^'=R=m (g-a)

Mass of person =50kg

Descending acceleration= 9m/s²

Acceleration due to gravity g= 10m/s²

Apparent weight of person R= m (g-a)

= 50 (10-9)=50N

Reading in weighing scale = 50/10 =5kg

This is a Short Answer type Questions as classified in NCERT Exemplar

explanation-total mass of bicycle and stone =m₁=50+0.5= 50.5kg

Velocity of bicycle u₁= 5m/s mass of stone m₂= 0.5kg

Velocity of stone u₂= 15m/s mass of girl and bicycle m= 50kg

 Also the speed of bicycle change when stone is thrown

According to conservation of linear momentum

m₁u₁=m₂u₂+mv

50.5 (5)= 0.5 (15)+50 (v)

V= 4.9m/s

Change in speed 5-4.9= 0.1m/s

This is a Multiple Choice Questions type Questions as classified in NCERT Exemplar

Answer- a, c

Explanation – mass m= 10kg

F₁ =6N, F₂= 8N

Resultant force F= $\sqrt[]{36+64}=10N$

a=f/m= 10/10= 1m/s²

let $\theta$ ₁ be the angle between R and F₁

tan $\theta$ ₁=8/6=4/3

_{$\theta$ 1}= tan $\theta$ ₁ (4/3) w.r.t F₁=6N

let $\theta$ ₂ be the angle between F and F₂

tan $\theta$ ₁=8/6=4/3

_{$\theta$ 2}= tan $\theta$ ₂ (4/3) w.r.t F₂=8N

This is a Multiple Choice Questions type Questions as classified in NCERT Exemplar

Answer- c, d

Explanation – m₁=m₂ = 50g= 1/20kg

Initial velocity u₁=u₂= 5m/s

Final velocity v₁=v₂= -5m/s

Time duration = 10^-3s

Change in linear ₁momentum = m (v-u)= 1/20 (-5-5)=-0.5N-s

Force = impulse /time=0.5/10^-3= 500N

So impulse and force are opposite in directions.

This is a Multiple Choice Questions type Questions as classified in NCERT Exemplar

Answer- b, c

Explanation- when A starts moving up

Mgsin ${\theta }_1+f=mgsin{\theta }_2$

mgsin ${\theta }_1$ + $\mu mgcos{\theta }_1$ = $mgsin{\theta }_2$

$\mu =\frac{\mathrm{s}\mathrm{i}\mathrm{n}{\mathrm{\theta }}_2-\mathrm{s}\mathrm{i}\mathrm{n}{\mathrm{\theta }}_1}{\mathrm{c}\mathrm{o}\mathrm{s}{\mathrm{\theta }}_1}$

When A moves downward f= $mgsin{\theta }_2-$ mgsin ${\theta }_1$ so clearly ${\theta }_2>{\theta }_1$