Secondary 3 Physics Q

BillaMax SG

A 50kg stone is being pushed with a force of 20 N. As a result, the stone is moving at a constant speed of 3m/s. What is the frictional force acting on the stone.

If I am not wrong the answer should be 20 Naccording to the 1st law of newton but why? I just don't get it.

TTFU SG

20 N. Because resultant force = 0N. The stone is moving at constant speed thus resultant force = 0 Thus the force u use is use to overcome the friction force of 20n

BillaMax SG

Question 2

The figure below shows the two horizontal forces acting on the car during a stage of the car motion.

<---------(5000N)-------- [Car] ---------(5000N)---------->

The forward force on the car is then reduced to 1000N, but the backward force remains as 5000N. Calculate the acceleration of the car now.

Ans. -2.67m/s^2

How to arrive at this answer?

TTFU SG

clues only like that ?

BillaMax SG

Yah. That is exactly the question for a book.

eagle SG

Question 2

The figure below shows the two horizontal forces acting on the car during a stage of the car motion.

<---------(5000N)-------- [Car] ---------(5000N)---------->

The forward force on the car is then reduced to 1000N, but the backward force remains as 5000N. Calculate the acceleration of the car now.

Ans. -2.67m/s^2

How to arrive at this answer?

Hi, we need the mass of the car as well because net F = ma

Without the mass of the car, we can only calculate the net force.

sunnyfhz SG

it is because the horizontal force = friction.

as the speed of the stone increases, the friction also increases. when friction is equal in magnitude to horizontal force, resultant force=0

at the start it was acceleration cos frictional force was less than horizontal force.

i didnt get it at the start too.:P

~PEPPER~ SG

My weakest subject.