In case the questions are hard to read: First Picture.) A cart is moving toward

Question

In case the questions are hard to read:

First Picture.) A cart is moving toward the right and speeding up, as shown in the diagram below. Assume that the cart is already moving at t1. If the positive direction is toward the right, what is the sign of force at t = 2s?

Second Picture.) A cart is moving toward the right and slowing down, as shown in the diagram below. Assume that the cart is already moving at t1 and t4. If the positive direction is toward the right, what is the sign of force at t = 2s?

Explanation / Answer

F = m a ==> m is + ==>

sign of F = sign of a

a = (v2 - v1 ) / t & t>0

a)

v is increase ==> v2 - v1 is + ==> a is + ==> F is +

b)

v is decrease ==> v2 - v1 is - ==> a is - ==> F is -

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