Answer:
Acceleration will increase.
Explanation:
The relation between force, mass and acceleration according to the Newton's second law of motion is given as:
F = ma
We are given that the driving force on the truck remains constant, so F is constant here. We can rewrite the above equation as:

Since, F is constant, the acceleration of the truck is inversely proportional to the mass.
There is a hole at the bottom of the truck through which the sand is being lost at a constant rate. Since, the sand is being lost, the overall mass of the truck is being reduced.
Since, the acceleration of the truck is inversely proportional to the mass, the reduced mass will result in an increased acceleration.
So, the acceleration of the truck will increase.
Spacecraft used is "Friendship 7". Hope it helps.
The electric field strength is 
Explanation:
The strength of the electric field produced by a single point charge is given by:

where
is the Coulomb's constant
q is the magnitude of the charge
r is the distance from the charge at which the field strength is calculated
For the charge in the problem, we have:
is the charge

Therefore, the electric field strength is

Learn more about electric fields:
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Answer:
159 N
Explanation:
The force of friction, Fr is a product of coefficient of feiction and the normal force. Therefore, Fr=uN where N is the normal force and u is coefficient of friction. Here, we have two coefficients of friction but since it is sliding, then we use coefficient of kinetic energy. Substituting 0.25 for u and 636 N for N then
Fr=0.25*636=159 N
Therefore, the force of friction is equivalent to 159 N