Which of the following is not a method of reducing friction?

Fill in the blanks:
$(a)$ $A$ load of $3 \, kg$ is suspended from a rope of $6 \, kg$. The tension at the top end of the rope is ...........
$(b)$ The effect produced by a force $F$ acting for a time $\Delta t$ is the same as that produced by a force $2F$ acting for a time ...........
$(c)$ Friction ........... due to excessive ironing.

Calculate the acceleration (in $m/s^{2}$) of the block and trolley system shown in the figure. The coefficient of kinetic friction between the trolley and the surface is $0.05$. (Given: $g = 10\; m/s^{2}$,mass of the string is negligible and no other friction exists).

$A$ solid ball is suspended from the ceiling of a motor car through a light string. $A$ transverse pulse travels at the speed $60 \text{ cm/s}$ on the string, when the car is at rest. When the car accelerates on a horizontal road, the speed of the pulse is $66 \text{ cm/s}$. The acceleration of the car is nearly $\left(g=10 \text{ m/s}^2\right)$ (in $\text{ m/s}^2$)

On which factors does the stopping distance of a vehicle depend?

Two carts are pushed apart by the explosion of a charge placed between them. $A$ cart of mass $100 \ kg$ stops after traveling a distance of $18 \ m$. What distance will a cart of mass $300 \ kg$ travel before stopping? The coefficient of friction $\mu$ between the carts and the ground is the same for both.