Lower Secondary Science

[Dr.033430Daniel]

jewelbox:

Hi, appreciate help on the following sec 1 question. Thanks

A car is moving a constant velocity along a straight road. the engine provides a forward thrust of T. The opposition drag due to the wind is W and the frictional force from the ground is F.

a) What is the difference between speed and velocity?

Speed is a scalar quantity and has only magnitude. Velocity is a vector quantity and has both magnitude and direction.

b) Determine the resultant force on the car. Hence, explain why the car is moving at a constant velocity.

The Resultant force = T-W-F = 0
If a car is moving at a constant velocity then there must be no resultant force. If there was any resultant force, there would be an acceleration.

c) At the speed of 80km/h, the total opposing force on the car is 200N. What is the thrust of the engine?

The thrust will also be 200N.

d) To beat a traffic light, the driver decided to increase the thrust of the engine to 250N. The total opposing forces is then increased by 10N.
i) Give a possible reason for the increase in the total opposing forces when the thrust of the engine is increased.

At a faster speed the force of air friction will be greater.

ii) Calculate the resultant force on the car.

250N – 210N = 40N

iii) The mass of the car is known to be 1,100kg. Using Newton's second law of Motion, calculate the acceleration of the car.

F = ma
40N = (1,100kg)a
a = 0.036 m/s2

[jewelbox]

Hello Dr Daniel

Thanks for your help with the above question.
:thankyou:

[jewelbox]

Hi, need help on the following sec 1 qns too. Thanks.


1. Michael pushed a box to the right with a horizontal force of 5.0 N. Jenny pushed with a horizontal force of 8.0 N on the same box in the opposite diretion at the same time. Assuming no other forces acts on the box.

a) find the resultant force acting on the box.
b) if the box weights 25.0N, calculate the acceleration produced by the resultant force in (a). (Take gravitational field strength on Earth to be 10N/kg).

2.Pile hammer are used to provide a firm base by driving piles into the ground, particularly on soft ground where buildings are being erected. The pile hammer has a mass of 3000kg. (Take g = 10N/kg)

a) calculate the work done when the hammer falls 150cm to hit the pile.

[jewelbox]

Continue…


3. John lifted a pail weighing 2N which also contained water of weight of 28N. The total work done by john in lifting the pail of water is 5.08kJ. find the distance the pail of water had been lifted.

[Dr.033430Daniel]

jewelbox:

Hi, need help on the following sec 1 qns too. Thanks.

1. Michael pushed a box to the right with a horizontal force of 5.0 N. Jenny pushed with a horizontal force of 8.0 N on the same box in the opposite direction at the same time. Assume no other forces act on the box.
a) find the resultant force acting on the box.

3N to the left

b) if the box weights 25.0N, calculate the acceleration produced by the resultant force in (a). (Take gravitational field strength on Earth to be 10N/kg).

Mass is 25N/(10N/kg) = 2.5kg
3N = (2.5kg)a
a = 1.2 m/s2

2.Pile hammers are used to provide a firm base by driving piles into the ground, particularly on soft ground where buildings are being erected. The pile hammer has a mass of 3000kg. (Take g = 10N/kg)
a) calculate the work done when the hammer falls 150cm to hit the pile.

The force of gravity on the pile hammer is 30,000N. The distance that force acts over is 1.5m. Work is equal to the force times the distance.
(30,000N) (1.5m) = 45000 Joules

3. John lifted a pail weighing 2N which also contained water of weight of 28N. The total work done by john in lifting the pail of water is 5.08kJ. find the distance the pail of water had been lifted.

5.08kJ = 5,080J = 30N (d)
d = 169 m

[jewelbox]

Hi Dr Daniel

Once again, many thanks for your solutions to the above questions; and the explanations that makes understanding the solutions easier.
:thankyou:

[genevieve08]

Dr.Daniel:

jewelbox:

Hi, need help on the following sec 1 qns too. Thanks.

1. Michael pushed a box to the right with a horizontal force of 5.0 N. Jenny pushed with a horizontal force of 8.0 N on the same box in the opposite direction at the same time. Assume no other forces act on the box.
a) find the resultant force acting on the box.

3N to the left

b) if the box weights 25.0N, calculate the acceleration produced by the resultant force in (a). (Take gravitational field strength on Earth to be 10N/kg).

Mass is 25N/(10N/kg) = 2.5kg
3N = (2.5kg)a
a = 1.2 m/s2

2.Pile hammers are used to provide a firm base by driving piles into the ground, particularly on soft ground where buildings are being erected. The pile hammer has a mass of 3000kg. (Take g = 10N/kg)
a) calculate the work done when the hammer falls 150cm to hit the pile.

The force of gravity on the pile hammer is 30,000N. The distance that force acts over is 0.15m. Work is equal to the force times the distance.
(30,000N) (0.15m) = 4500 Joules

3. John lifted a pail weighing 2N which also contained water of weight of 28N. The total work done by john in lifting the pail of water is 5.08kJ. find the distance the pail of water had been lifted.

5.08kJ = 5,080J = 30N (d)
d = 169 m

I would like to verify that distance should be 1.5m and not 0.15m. Your advice please.

[anneshirleygilbert]

Can somebody please help me with this question:


A solution is made up of _____________

A. only one solute and one solvent
B. one or more solute and one or more solvent
C. only one solute and one or more solvent
D. one or more solute and only one solvent

The answer key is (A), but it is possible to dissolve some salt and sugar (solutes) in water (solvent) and that would make (D) the correct answer, won’t it?

Please help. TIA

[dioprem]

anneshirleygilbert:

Can somebody please help me with this question:


A solution is made up of _____________

A. only one solute and one solvent
B. one or more solute and one or more solvent
C. only one solute and one or more solvent
D. one or more solute and only one solvent

The answer key is (A), but it is possible to dissolve some salt and sugar (solutes) in water (solvent) and that would make (D) the correct answer, won't it?

Please help. TIA

Strictly speaking, a solution can have only 1 solvent, but multiple solutes. An example of a solution with multiple solutes is air. So yes, D would be the answer.

Hope this helps.

[anneshirleygilbert]

Thank you, dioprem for your help.


I hold the same view as you about solution having one solvent and multiple solutes. But, does Secondary School science put air as a solution? I thought it’s a mixture?? Trying to get my terminology right. Please help. TIA