Answer:
-4.0 N
Explanation:
Since the force of friction is the only force acting on the box, according to Newton's second law its magnitude must be equal to the product between mass (m) and acceleration (a):
(1)
We can find the mass of the box from its weight: in fact, since the weight is W = 50.0 N, its mass will be
And we can fidn the acceleration by using the formula:
where
v = 0 is the final velocity
u = 1.75 m/s is the initial velocity
t = 2.25 s is the time the box needs to stop
Substituting, we find
(the acceleration is negative since it is opposite to the motion, so it is a deceleration)
Therefore, substituting into eq.(1) we find the force of friction:
Where the negative sign means the direction of the force is opposite to the motion of the box.
Formula for time
t=d/s
so…
t= 48m/4m/s
the two ms cancel each other out and ur left with s
t=12s
- The mechanic did 5406 Joules of work pushing the car.
That's the energy he put into the car. When he stops pushing, all the energy he put into the car is now the car's kinetic energy.
- Kinetic energy = (1/2) (mass) (speed²)
And there we have it
- The car's mass is 3,600 kg.
- Its speed is 'v' m/s .
- (1/2) (mass) (v²) = 5,406 Joules
(1/2) (3600 kg) (v²) = 5406 joules
1800 kg (v²) = 5406 joules
v² = (5406 joules) / (1800 kg)
v² = (5406/1800) (joules/kg)
= = = = = This section is just to work out the units of the answer:
- v² = (5406/1800) (Newton-meter/kg)
- v² = (5406/1800) (kg-m²/s² / kg)
= = = = =
v = √(5406/1800) m/s
<em>v = 1.733 m/s</em>
Resistance of a wire is directly proportional to its length and inversely proportional to the square of its radius.
Thus, if the length is doubled, and the radius is halved:
R₂ = 2R₁/(1/2)²
R₂ = 8R₁
Therefore the resistance increases eight times.
