A physics problem simple movement for junior high school

Answer D Analysis: Taking the passenger as the reference, the relative direction of movement of the motorcycle is the northwest direction, and the relative movement speed is decomposed into the velocity v0 in the west direction and v1 in the north direction.

Let the speed of the car be V, and the actual speed of the motorcycle V3 is decomposed into the velocity V4 in the direction of due west, and V5 in the direction of due north, then there is V4-V=V0>0 So the speed of the motorcycle V3 must be greater than the speed of the car, option D is correct, and B is wrong.

When V4 >> V1, if V4-V=V0, V5-0=V1, and V0=V1, then the motorcycle is northwest relative to the car, but because the actual westward V4 of the motorcycle is much greater than V5 in the due north direction, the actual speed V3 can tend to be due west, and options A and B are incorrect.

d Passengers sitting in a westbound car and seeing a motorcycle moving northwest indicate that the speed of the vehicle must be less than the speed of the motorcycle relative to the ground, because this can only happen if there is a positive speed difference between the motorcycle and the car.

Hope o ( o

dRelative to the ground, the speed of the vehicle must be less than the speed of the motorcycle.

The car that should be a passenger is in motion, and only the speed of the vehicle must be less than the speed of the motorcycle can produce a passenger sitting in a car heading west to see a motorcycle moving northwest.

Choose C, believe me, 99 points in physics in the high school entrance examination.

f=g=mg=2000kgx10n kg=20000n, regardless of rising or falling, are the tension and gravity as the balance force, both are equal, find some balance force information, I hope to help understand, several forces acting on the same object, if the object is still or becomes in a state of rest or uniform linear motion, then the resultant force of these forces is zero, we say that these forces are balanced.

Judge balance.

1. Two forces act on the same object. 2. Each pair of forces or each pair of resultant forces is in the same straight line, opposite in direction, and equal in magnitude. (Both the net force is zero) (equal size, same line, opposite direction) 3. The object is in a state of stationary or uniform linear motion.

and interaction forces).

Classification of Equipoise.

Equilibrium forces are also divided into multi-force balance and two-force balance, and the conditions for two-force balance are: the two forces are equal in magnitude, opposite in direction, acting on a straight line, and acting on the same object. Multi-force equilibrium is similar.

Since it is a uniform motion, then the pulling force is equal to the gravitational force, which is 2000x10=20000n

In both cases, the container is balanced by force, and the pulling force is equal to the gravity.

Both are moving in a straight line at a uniform velocity, and the force on the object is balanced, so the pulling force is equal to the gravitational force.

t=mg gives t=20000n

1. Ask for the time when he then rides at a speed of 18 km/h t=s vs=12km-15km h 12 60h=9kmt=9km 18km h=

Average speed = total distance Total time = 12 km [(12 + 6 + 30) 60] = 15 km h

2. Total time = 12 + 6 + 30 = 48 minutes Arrive on time at the agreed arrival time at 9:48.

With a distance of 18 km is 12-15*

So time. A total of 9:48 was agreed

So an average of 12 km h

115x12/60=3km

12-3) 18=hours.

Average speed = 12 (12 + 6 + 30) =

2 o'clock is 9:48.

1. The first 12 minutes of riding 15 kilometers * 12 60 hours = 3 kilometers, the remaining 9 kilometers take 9 18 = hours.

Therefore, the whole process is shared 12 + 6 + 30 = 48 minutes. The average speed is 12 km (48 60) hours = 15 km h.

The agreed arrival time is 9 a.m. + 48 minutes = 9:48 a.m.

First find the time of arrival that he originally planned, s=vt t=v s find the distance traveled at 15km h, find the time taken in the remaining distance, and then the time taken is known, and then the average speed is the total distance compared to the time used.

15km|h=250m|min 18km|h=300m|min solution: 250x12=3000m 12km-3000m=9000m9000m divided by 300=30min

The total time is 12+6+30=48min=

The average speed of 12km divided by 48 is 250m|min is known as 15km|h

The arrival time is 9:48 a.m.

Without taking into account the drag of air on the bullet, the calculation is as follows:

t=51/340s

v bullet =

1 When rowing in a lake, the driving force that moves the boat forward is ( d ).

a.The thrust of the paddle stroke bThe thrust of the water directly against the ship cMan-to-ship thrust dThe thrust of water against the oar.

2.What forces are used on a football kicked into the air (b).

a. by the force of the foot and by gravity b. by gravity c by the force of the foot only d. not by any force.

3.When a car is moving at a speed of 6 meters and 4 meters and seconds respectively, its inertia is (a).

a.Just as big; b.The speed is 4 meters per second; c.The speed is 6 meters per second; d.Can't compare.

4.The passenger in a car standing at a constant speed is subjected to several forces (b).

One by one.

5 Two students, A and B, pull the dynamometer in opposite directions, and each exert 200 N force. Then the indication of the dynamometer is (b).

A, 100 N B, 200 N C, 0 N D, 400 Niu.

6.An object is acted upon by two forces, and the three elements of these two forces are exactly the same, then these two forces (b).

A must be a balance B must not be a balance c may be a balance d d cannot be judged.

20 In studying the "relationship between motion and force," we have followed in the footsteps of physicists and designed such "inclined plane" experiments:

1) as shown in the figure, let the dolly slide down from the inclined plane and move along the horizontal plane, is to make the trolley move in the horizontal plane, the force and force that the vertical direction is subjected to are balanced, and the equivalent trolley is only subjected to the frictional force in the horizontal direction

2) let the trolley slide down from the position of the same inclined plane from the standstill every time, so that the trolley has the same speed when sliding to the bottom end

3) reduce the roughness of the horizontal plane in the figure, compare the maximum distance of the trolley sliding on different surfaces, it can be obtained: under the condition of the same initial velocity, the smoother the horizontal plane, the more frictional force the trolley is subjected to, and the distance of the trolley movement

4) further reasoning shows that if the horizontal plane is absolutely smooth, then the trolley will move on the horizontal plane

1) Heavy support (2) Same (3) Small length (4) Uniform straight line.

Car A drove to a certain place at a speed of 30 kilometers and set off 3 hours later. Car B chased car A at a speed of 45 kilometers per hour from the starting point of car A and asked; How long does it take to catch up with car A? How many kilometers did the two cars travel when they caught up?