Class 11th

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

Explanation – as body moving with uniform acceleration a=0

The sum of forces is zero F₁+F₂+F₃=0

a)let F₁, F₂, F₃ be the three forces passing through the point . let F₁and F₂ be in the plane A

so F₃ =- (F₁+F₂) so F₃ is also in plane A.

b)consider the torque of the forces about P . since all the forces pass through P the torque is zero

torque = OP (F₁+F₂+F₃)

since F₁+F₂+F₃=0 so torque =0

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

Explanation -initial speed of coin u= 20m/s

Acceleration of elevator =2m/s² acceleration due to gravity = 10m/s²

Effective acceleration =g+a=12m/s²

We know that v=u +at

0= 20+ (-12)t

So t= 20/12=5/3 s

Time of ascent = time of descent

Total time coin fall back into hand = (5/3+5/3)=10/3s=3.33s

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

Explanation- from the diagram x= t=dx/dt=1m/s

So a_x= 0

From the diagram y =t²

dy/dt=2t  or a_y=d²y/dt²=2m/s²

I_y= ma_y=500 (10^-3) (2) =1N

F_x=ma_x=0

F= $\sqrt[]{F_x^2+F_y^2}$ = 1N

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

Explanation- mass of gun =100kg

Mass of ball =1kg and height of cliff = 500m

So horizontal distance travelled by the ball is x = 400m

So h =1/2gt²

500= $\frac{1}{2}10\left(t\right)$ ² so t= 10s

X=ut then u= 400/10=40m/s

 According to principle of conservation pf momentum

Mv=mu

V= 40/100= 0.4m/s

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

Explanation-given mass of the block =M

Coefficient of friction between block and the wall = $\mu$

In equilibrium  condition vertical and horizontal component balance each other

So f=mg

And F=N but the force of friction f= $\mu N=\mu F$

  $\mu F=Mg$

F= Mg/ μ $\mu$

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

Explanation- in equilibrium, The force mgsin $\theta$ acting on the block A is parallel to the plane should be balanced by the tension in the string

mgsin $\theta =T=F$

and for block B, w=T=F

 from these two above equation 

w=mgsin $\theta$ = 100sin30= 100 (1/2)=50N

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

Explanation- m₁= 5kg, m₂= 3kg

And g= 9.8m/s² and a= 2m/s²

For the upper block T₁-T₂-5g=5a

T₁-T₂= 5 (g+a)

For the lower block T₂-3g =3a

T₂=3 (g+a)=3 (9.8+2)=35.4N

T₁=T₂+5 (g+a)=94.4N

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

Explanation – when the lower thread CD is pulled with a * the thread Cd itself break because the thread CD is not transmitted to the thread Ab instantly.