Question

1. A speed-time graph shows that a car moves at 20 m/s for 15 s. The car’s speed then steadily decreases until it comes to a stop at 40 s. Which of the following describes the slope of the speed-time graph from 15 s to 40 s?

A. linear, sloping downward
B. linear, sloping upward
C. linear, horizontal
D. curved, upward

2.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 dividing the river current vector by the boat’s velocity vector
B. by multiplying the vectors
C. by adding the vectors
D. by subtracting the river current vector from the boat’s velocity vector

Answer 1

1. linear, sloping downward (option A)
2. by adding vectors (option C)

Answer 2

A. linear, sloping downward

Step-by-step explanation:

As we know that the speed of the car is decreasing to zero from initial value of speed at constant rate

So we can say

`(dv)/(dt) = - C`

so the slope of the velocity and time graph will be constant and negative

so here the graph would be linear and sloping downwards

Answer:

C. by adding the vectors

Step-by-step explanation:

As we know that the boat is moving in the direction of river current with relative speed 10 m/s

so here we can say

`\vec v_(br) = \vec v_b - \vec v_r`

so the velocity of boat is given as

`\vec v_b = \vec v_(br) + \vec v_r`

so we have to add the relative velocity vector with the velocity vector of the river