1. A block of mass m is pulled at constant velocity along a flat floor by a forc

Question

1. A block of mass m is pulled at constant velocity along a flat floor by a force T which is at an angle from the flat floor. The vertical/normal force exerted on the block by the floor is equal to:
A.   mg       B. mg + T cos       C. mg - Tcos       D. mg - Tsin       E. mg + Tsin

1 (b).When is a scalar/dot product of two vectors equal to zero?
A. Never       
B. If they both point in the same direction
C. If they both point in the opposite direction
D. If they are perpendicular to each other
E. Both (B) and (C) are correct answers

Explanation / Answer

(D) mg - T sin(theta)

explanation:

the sum of forces in Y direction is:

N - mg + T sin(theta) = 0

N = mg - T sin(theta)

1(b) If they are perpendicular to each other

explanation:

the dot product is given by:

A.B = lAl lBl cos(theta)

cos90 = 0

Hence, dot product of two vectors if zero if they are perpendicular to each other

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