Mechanics | Relativity Answers

A 28.0-kg block is initially at rest on a horizontal surface. A horizontal force of 80.0 N is required to set the block in motion, after which a horizontal force of 57.0 N is required to keep the block moving with constant speed.
(a) Find the coefficient of static friction between the block and the surface.
(b) Find the coefficient of kinetic friction between the block and the surface.

The force exerted by the wind on the sails of a sailboat is Fsail = 400 N north. The water exerts a force of Fkeel = 190 N east. If the boat (including its crew) has a mass of 260 kg, what are the magnitude and direction of its acceleration?
magnitude m/s2
direction ° north of east

What was the average speed of the man in m/min? (68 m/min)
A boy runs at 5.0 m/s [30° S of W] for 2.5 minutes and then he turns and runs at
3.0 m/s [40° S of E] for 4.5 minutes.
A. What was his average speed?
B. What was his displacement?

A train starts from rest at station A and is uniformly accelerated until it reaches speed of 108km/h. It then travel at this speed until the breaks are applied and the train is then uniformly retarded until it stops at station B. The magnitude of this retardation is twice the magnitude of the initial acceleration. The distance between the stations is 12km and the time taken for the journey is 10minutes. Find the
1. Time spent of each of the three stages of the journey.
2. Initial acceleration
3. Final retardation.
Question 2
A stone 0.2kg is dropped over a cliff. Write down the force in Ns which acts on it and hence find its momentum after 3s. Take g=10m/s

An apple falls from a tree and hits the ground 13.4 m below. With what speed will it hit the ground? The acceleration of gravity is 9.8m/s

Given: The battleship and enemy ships A
and B lie along a straight line. Neglect air
friction.
A battleship simultaneously fires two shells
at these two enemy ships.from a cliff 33.8 m high. At the level of the
sea, a rock sticks out a horizontal distance of
8.29 m. The acceleration of gravity is 9.8 m/s2. With what minimum horizontal velocity
must the cliff divers leave the top of the cliff if
they are to miss the rock?
Answer in units of m/s.

A sinusoidal wave of frequency f=100 hz propagates in a medium with a speed 12m/s.Give the expressions of the distance separating:
A) two in-phase points
B) two anti-phase points

While standing on the ground, you want to throw a textbook straight up to a classmate standing by a window 12.p m above you. With what velocity must you throw the book so that the maximum height it reaches is the height of the window?

1. A man start from point A and walks a distance of 3.0km due northeast to point B. from point B he then walk 4.0km due Southeast to point X. Calculate the shortest distance between point A and X.

2. Two cars A and B move with a velocity of 60km north and 40 km north respectively. What is the velocity of B with respect to A?

3. Two forces 5N and 8N act at the same point at an angle of 45 degree to each other. Calculate the magnitude of their resultant.

4. A force of 20N act at an angle of 30 degree to the horizontal. Determine the vertical component of the force.

5. The forces of magnitude 30N and 40N act at an angle of 90degree to each other. Calculate the magnitude of their resultant.

6. Two forces whose resultant is 100 N are perpendicular to each other. If the horizontal force make an angle of 60degree with the resultant. Calculate it's magnitude.

7. Two forces of magnitude 8N and 5N act at an angle of 60 degree to each other. Find the magnitude.

In the 2016 Olympics in Rio, after the 50 m freestyle competition, a problem with the pool was found. In lane 1 there was a gentle 1.2 cm/s current flowing in the direction that the swimmers were going, while in lane 8 there was a current of the same speed but directed opposite to the swimmers' direction. Suppose a swimmer could swim the 50.0 m in 25.0 s in the absence of any current.
How would the time it took the swimmer to swim 50.0 m change in lane 1?