I tried my best but coudnt find answers to these questions!! help pls!
Know the reason, tell me!!
1. A hollow ball is release from the bottom of a pool. After a short time it rises at a constant speed. What is the resultant force then acting on the ball
2. When a block of wood of mass 2kg was pushed along the horizontal flat surface of a bench, the friction force measured was 4n. when the block was pushed along the same bench with a force of 10 N, find the motion?
3. A block of mass 6 Kg is pulled across a rough surface by a 54 N force, against a friction force?
The acceleration of the block is 6m/s (squared). What is the value of F?
4.A person just supports a mass of 20 KG suspended from a rope.
What is the resultant force acting on the mass?
5. The total weight of a gas-filled ballon is 1500N. The ballon rises at a constant speed of 3m/s.
What is the resultant force acting on the balloon while it is rising?
6. An experiment is carried out by an astronaut on the surface of the moon. Acoin and a feather are dropped at the same instant from the same height?
Which item(s) will reach first and why?
And mainly how do you use the two methods such as tip-to-tail method and the other one? can you tell me a website where it is demonstrated clearly??
(1)The hollow ball is less dense than water, so it will rise very quickly. But water resistance against the motion of the ball increases with the speed of the ball. When the downward water resistance together with the weight of the ball is equal to the upthrust acting on the ball, net force = 0 N. Remember net force = mass x acceleration. Since net force is zero, acceleration is zero. So you add nothing to the speed. The speed of the ball remains constant from this moment onwards.
ReplyDelete(2)Net force = Applied force - frictional force
= 10 N - 4 N = 6 N.
By Newton's second law of motion, net force = mass x acceleration
6 N = 2 kg x a
a = 6/2 = 3 metres per second squared.
(3) If you know m = 6 kg and a = 6 metres per second squared, then by Newton's second law of motion, F = ma = 6 x 6 = 36 N
Frictional force = Applied force - Net force
= 54 N - 36 N = 18N
(4) Weight of the 20 kg mass, W = mg = 20 x 10 = 200 N (assume g = 10 N/kg or 10 metres per second squared)
ReplyDeleteTension in the supporting rope acting upwards = 200N = Weight of object acting downwards.
So the resultant force = 200 N - 200 N = 0 N.
(5) If the balloon is rising at constant speed, it is not accelerating or we say, its acceleration, a = 0 metres per second squared. Therefore the net force, resultant force or accelerating force (all 3 are different names for the same force) = mass x acceleration = 0 N.
(6) On the moon, there is no air, hence no air resistance. Therefore both the coin and the feather dropped from the same height at the same instant will reach the ground at the same time, since they are subjected to the same acceleration due to moon's gravity.
Go to Shoba's blog to learn. Anyway, Jasmine Chan asked the same question and I have already answered her question. If you watch the University of California's video clip on Dynamics, you will understand why the resultant of 2 forces is given by the diagonal of the parallelogram in between the 2 forces.
ReplyDeletek sure
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