Question

HELP NEEDED ASAP
I have like an hour and a half to answer these

A passenger in the rear seat of a car moving at a steady speed is at rest relative to

A. a car coming from the opposite direction.
B. the front seat of the car.
C. a pedestrian on the corner ahead.
D. the side of the road.

A river current has a velocity of 10 km/h relative to the shore, and a boat moves in the same direction as the current at 10 km/h relative to the river. How can the velocity of the boat relative to the shore be calculated?
A. by adding the vectors
B. by multiplying the vectors
C. by subtracting the river current vector from the boat’s velocity vector
D. by dividing the river current vector by the boat’s velocity vector

A horizontal line on a distance-time graph means the object is
A. slowing down.
B. moving faster.
C. at rest.
D. moving at a constant speed.

A motorcycle travels 850 meters in 14 seconds. What is its average speed?

Speed is the ratio of the distance an object moves to
A. the motion of the object.
B. the amount of time needed to travel the distance.
C. the direction the object moves.
D. the displacement of the object.

A train travels 62 kilometers in 4 hours, and then 93 kilometers in 5 hours. What is its average speed?

Answer 1

b,c,c,d,60.7142....m/s,b,15.5kph

Answer 2

1. B. the front seat of the car.

The passenger in the rear seat of the car is at rest relative to an object which is moving at his same speed. Since the car is an coeherent object, all the parts of the car move at same speed, so the front seat moves at same speed as the rear seat. Therefore, the passenger in the rear seat is at rest relative to the front seat of the car.

2. A. by adding the vectors

The river current is moving with velocity $v_c=10 km/h$ in a certain direction relative to the shore. The boat is moving with velocity $v_b=10 km/h$ relative to the current, and in the same direction as the current, Therefore, the total velocity of the boat relative to the shore will be equal to the sum of the two vectors (because they are in the same direction):

$v=v_B+v_c = 10 km/h + 10 km/h = 20 km/h$

3. C. at rest

A distance-time graph shows the distance travelled by an object as a function of the time passed. In such a graph, the slope of the curve represents the speed of the object. In fact, the speed of an object is defined as

$v=\frac{d}{t}$

where d is the distance travelled and t the time taken. However, we see that this definition corresponds to the slope of the curve in the distance-time graph, because the distance is the increment in the y-variable, while the time is the increment in the x-variable:

$v=\frac{\Delta y}{\Delta x}$

Therefore, a horizontal line means slope zero, therefore zero velocity: so, the object is at rest.

4. 60.7 m/s

The average speed of the motorcycle is equal to the ratio between the distance travelled and the time taken:

$v=\frac{d}{t}$

In this problem,

d = 850 m

t = 14 s

Therefore, the average speed is

$v=\frac{850 m}{14 s}=60.7 m/s$

5. B. the amount of time needed to travel the distance.

Correct: speed is defined as the ratio between the distance travelled by an object and the time required to travel that distance. In formula, this means:

$v=\frac{d}{t}$

where d is the distance travelled and t the amount of time needed.

6. 17.2 km/h

The average speed is given by the ratio between the total distance and the total time taken.

The total distance travelled by the train is:

$d=62 km+93 km=155 km$

The total time taken is:

$t=4h+5h=9h$

So, the average speed is

$v=\frac{d}{t}=\frac{155 km}{9 h}=17.2 km/h$