Answer:
If child weight is equal to rope force then child will move with uniform speed
or we can say that the child will remain at rest in his position
Explanation:
As we know that child is hanging by rope
so here there will be two forces on the child
1) Weight or gravitational force which act vertically downwards
2) Tension in the rope which act vertically upwards
Now if child will accelerate upwards then tension force must be more than the weight of the child
If tension force is less than the weight then child will decelerate and his speed will decrease
if tension force is equal to child weight then in that case the child will remain at rest or it will move with same speed
Wave speed = (wavelength) x (frequency)
= (4 m) x (2 /sec)
= 8 m/sec
use F = ma
F : force m : mass a : acceleration
so
f = 5kg * 20 m/s2 = 100 N
Answer:

Explanation:
Assume that the distance travelled initially is d.
In order to stop the block you need some external force which is friction.
If we use the law of energy conservation:

a)
Looking at the formula you can see that the mass doesn't affect the distance travelled, as lng as the initial velocity is constant (Which indicates that the force must be higher to push the block to the same speed) therefore the distance is the same.
b) If the velocity is doubled, then the distance travelled is multiplied by 4, because the distance deppends on the square of the velocity.
Answer:
72km
Explanation:
30 mins --> 30 x 60 s = 1800 s
Distance --> Speed x Time
= 40m/s x 1800s
= 72 000 m
= 72 km (1km is 1000m)