Q. A block slides down a frictionless incline of angle 30 degrees. If the incline has a coefficient of kinetic friction of 0.2, what is the acceleration of the block?
A.4.9 m/s²
B.3.9 m/s²
C.2.9 m/s²
D.1.9 m/s²
Solution
Net force = mg sin(30) - μmg cos(30). Acceleration a = (mg sin(30) - μmg cos(30))/m = g(sin(30) - μ cos(30)). Substituting g = 10 m/s² gives a = 10(0.5 - 0.2 * √3/2) = 4.9 m/s².
Q. A boat can travel at 10 km/h in still water. If it is moving downstream in a river flowing at 5 km/h, what is the speed of the boat relative to the riverbank?
A.5 km/h
B.10 km/h
C.15 km/h
D.20 km/h
Solution
Speed downstream = Speed of boat + Speed of river = 10 km/h + 5 km/h = 15 km/h.
Q. A boat can travel at 12 km/h in still water. If it is going downstream in a river flowing at 3 km/h, what is the speed of the boat relative to the riverbank?
A.9 km/h
B.12 km/h
C.15 km/h
D.3 km/h
Solution
Speed of boat downstream = Speed of boat + Speed of river = 12 km/h + 3 km/h = 15 km/h.
Q. A boat can travel at 12 km/h in still water. If it is going downstream in a river flowing at 4 km/h, what is the speed of the boat relative to the riverbank?
A.8 km/h
B.12 km/h
C.16 km/h
D.20 km/h
Solution
Speed of boat downstream = Speed of boat + Speed of river = 12 km/h + 4 km/h = 16 km/h.
Q. A boat can travel at 12 km/h in still water. If it is moving downstream in a river flowing at 4 km/h, what is the speed of the boat relative to the riverbank?
A.8 km/h
B.12 km/h
C.16 km/h
D.4 km/h
Solution
Speed of boat relative to riverbank = Speed of boat + Speed of river = 12 km/h + 4 km/h = 16 km/h.
Q. A boat can travel at 15 km/h in still water. If it takes 2 hours to travel upstream and 1.5 hours to travel downstream, what is the speed of the current?
A.2 km/h
B.3 km/h
C.4 km/h
D.5 km/h
Solution
Let speed of current = x. Upstream speed = 15 - x, Downstream speed = 15 + x. (2 hours)(15 - x) = (1.5 hours)(15 + x). Solving gives x = 3 km/h.
Q. A boat travels 30 km upstream and 30 km downstream in a total time of 6 hours. If the speed of the boat in still water is 10 km/h, what is the speed of the current?
A.2 km/h
B.3 km/h
C.4 km/h
D.5 km/h
Solution
Let speed of current = x. Time upstream = 30/(10-x), downstream = 30/(10+x). Total time = 6 hours. Solving gives x = 2 km/h.
Q. A boat travels across a river with a speed of 4 m/s relative to the water. If the river flows at 3 m/s, what is the resultant speed of the boat relative to the riverbank?
Q. A boat travels across a river with a speed of 8 km/h relative to the water. If the river flows at 6 km/h, what is the speed of the boat relative to the riverbank?
A.8 km/h
B.10 km/h
C.14 km/h
D.6 km/h
Solution
Speed of boat relative to riverbank = √(8^2 + 6^2) = √(64 + 36) = √100 = 10 km/h.
Q. A body moves in a straight line with a uniform acceleration of 2 m/s². If its initial velocity is 5 m/s, what will be its velocity after 10 seconds?
A.25 m/s
B.20 m/s
C.15 m/s
D.10 m/s
Solution
Final velocity = initial velocity + acceleration * time = 5 + 2 * 10 = 25 m/s.
